Men's Fitness: 39 things you should never do

As a guy, there are some things you instinctively know you should never do. No junior-high coach ever had to take you aside and tell you, for example, "Now, listen carefully, son: Never take the urinal directly between two other guys if there's one open on the end." The no-adjacent-peeing rule is something you just know (along with every other guy in the Terminal 4 men's room at O'Hare).

Of course, not all knowledge is so inborn. But fortunately, you can steer clear of trouble by following a few guidelines, detailed here. Consider this compendium of "nevers" your personal rulebook. Never stray from it, and you'll be fine.

Never SHAVE YOUR HEAD IN THE MIDDLE OF SUMMER

1 Since your face will already be several shades darker than your head, you'll end up looking like you have a white swim cap on your noggin. A more serious reason: The sensitive skin on your scalp hasn't built up any resistance to the sun's harmful rays. "No one knows why, but skin cancers on the scalp are far more aggressive than those anywhere else on the body," says Arnold Klein, MD, a Southern California-based dermatologist.

At Home

2 Never skip breakfast. The morning is when your body really needs calories - and if you don't eat, it will break down your muscles to get them. Also, if you skip the a.m. meal, you'll build steam until lunch, when your body will go into full-tilt "famine mode" and you'll devour everything in sight. Bonus: Studies show that people who eat a healthful, low-fat breakfast are more likely to eat healthfully throughout the day.

3 Never try to neutralize odors with air-freshening sprays. Air fresheners don't get rid of smells in the air; all they do is cover them up and make you less sensitive to them. What's more, many leading brands contain potentially carcinogenic compounds as well as "natural" oils that can be harmful to inhale. If the air in your home smells bad, buy an electric air cleaner with a HEPA filter - or at least do the laundry.

4 Never go more than 24 hours without flossing your teeth. Everyone's heard this message, but many don't realize its importance. Your dentist will be happy to tell you that unflossed pearly whites can lead to excess plaque buildup and gum degeneration, possibly necessitating painful tooth scraping and even excruciating root-canal surgery.

5 Never take antibiotics for a cold, Unless you have a sinus infection, they won't make you feel any better. And the more often you use antibiotic medications, the less effective they're likely to be when you really need them.

6 Never use anti-redness eyedrops for more than 72 hours. Like those in anti-sniffle nose sprays, the decongestants in eyedrops can have a "rebound" effect, causing the problem to come back worse than before. When eyedrops are overused, they can produce a kind of chronic redness called non-infectious conjunctivitis. Drug-free "artificial tears" can help with red eyes, as can cold compresses, getting enough sleep and not staring at a computer too long.

7 Never pay your phone bill (or any bill, for that matter) without reading it carefully. Doing so will help you avoid being "slammed" (having your long-distance carrier switched without your permission, resulting in higher rates) or "crammed" (being billed for services that you didn't authorize).

8 Never put up with unwanted telemarketing calls, The first time someone calls you, simply request that your number be put on the "do not call" list. Find out whether the telemarketer's employer makes calls for other companies (a common practice) and insist that they never call you on behalf of any organization.

9 Never take food cravings at face value. When you're dying for candy or a soda, your body is actually asking for energy, not sugar. "if it's the middle of the afternoon and you really want a candy bar, you have to ask yourself, 'Did I eat enough lunch today?' Probably not," says Nancy Clark, RD, author of Nancy Clark's Sports Nutrition Guidebook. Beat those cravings by eating smaller meals more frequently throughout the day - at, say, three-hour intervals.

10 Never take medications together with grapefruit juice without a doctor's OK. Chemicals in grapefruit juice have an odd effect on medicines, possibly because they interfere with liver enzymes. This can cause either decreased or increased concentration of a drug in your bloodstream, making it less effective or increasing the risk of side effects.

Never TAN IN A TANNING BOOTH

11 There really is no such thing as a safe tan - in fact, a U.S. government panel recently recommended putting ultraviolet light, whether from the sun or a tanning lamp, on the official list of known carcinogens. The booths that emit only UVA radiation are no safer - it's even more likely than UVB to cause melanomas. If you must have a tan, get it from a bottle.

12 Never completely obliterate fat from your diet. Most fit guys follow a simple nutrition parameter: Fat is bad. But this isn't the case. A study conducted at SUNY-Buffalo showed that athletes' performance and immune systems suffered when they got less than 15 percent of their daily calories from fat. Try to get 20 to 25 percent of your calories from fat, focusing on natural, non-saturated choices such as olive oil, avocados, nuts and cold-water fish such as salmon.

13 Never eat canned tuna packed in oil. Even if you drain the oil first, the fish can still have 50 percent more calories and several times the fat content of the water-packed variety. And while you'll still get some fat from water-packed tuna, it's all from the fish's natural health-promoting oil.

On the job

14 Never pick up the phone when you're annoyed or angry. Instead. take a breath first, and smile when you answer the phone or place a call, recommends Jennifer Maxwell Parkinson. president of Look Consulting International. a New York-based image-and-communication consulting firm The idea: You can't sound perturbed when you have a grin on your face.

15 Never say, "I have no idea." To your boss or a client (or even your subordinates), it makes you sound uninformed and - even worse - unmotivated. If you're pressed for information you don't have, reply, "Let me look into that and get back to you with the latest data." Then do it.

16 Never accept a lump-sum distribution of your retirement-plan savings when changing jobs - you'll face serious tax consequences up front, and you'll forfeit all of the earnings you might have had for retirement. If you can't keep your cash in your old employer's program or transfer it to your new company's plan, roll it directly into an IRA.

In a casino

17 Never buy insurance in blackjack unless you're counting cards and know the exact proportion of 10s to cards of lesser value in the deck. Otherwise, you're playing into the hands of the house - and they don't wear kid gloves.

18 Never pick 15 out of 15 at Keno. The odds of winning are about one in 430 billion, or the same likelihood that it was your blood in O.J.'s Bronco.

At the bank

19 Never pay a monthly fee for a checking account. "Free checking accounts are everywhere," says Larry Roth, author of The Simple Life. Roth recommends contacting several banks and credit unions and negotiating a deal that suits your needs. It can be quite simple: Many banks offer free checking to customers whose employers deposit paychecks directly into the account.

Surfing the web

20 Never use your credit card on the Internet if you're not on an SSL (secure) server. Many websites mention whether they're secure. If you can't determine the security of a site, check for a closed padlock icon in the lower-left corner of your screen. (The icon will often stay unlocked until you've opened the order page.) Although it also helps to know the organization you're dealing with, discretion is always the best policy.

At the gym

21 Never sign up for a gym membership on the first visit. There's always a better price, says Sharin Abadian, general manager of Bally's Total Fitness in McLean, Virginia. "Deal to get the price to where you want it, then leave," Abadian says. "You should receive a call within a week offering a better price than the one you originally wanted - especially toward the end of the month, when clubs need to meet their monthly numbers."

22 Never wear a weight belt unless you're performing a movement that puts a direct compressive load on your spine. According to trainer Christopher M. Lockwood, CSCS, studies have shown that wearing a belt during workouts may weaken the abdominals, which can result in back problems. "Instead of wearing a belt, try consciously contracting your abs during a lift," Lockwood says.

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23 Never eat a large meal before working out. Food requires energy to digest. The more food you eat, the more energy gets diverted toward digestion - and not your workout. "If you're going to eat a large meal before working out, make sure it's at least one to three hours beforehand," says Timothy Moore, PhD, a Los Angeles-based fitness consultant and former competitive triathlete.

24 Never wear running shoes on a heavy leg day. "Running shoes provide great cushioning for running," says certified personal trainer William Finney, "but that robs you of some of your power during heavy squats." Running shoes also lack lateral stability, which is a problem if you're doing heavy lunges or farmer's walks. Instead, wear firm, fiat-soled shoes.

25 Never perform abdominal movements in a fast or uncontrolled manner. To get the most out of any abdominal movement, you have to go slowly. "The range of motion of the abdominal muscles is very short," says Ray Velasquez, a Los Angeles-based personal trainer. "Focus on rolling your abdominals up as you contract them. Using momentum to perform an abdominal movement is a waste of time because the duration of the stress being placed on the abdominals is so short."

26 Never skip a meal after a workout. "Once you leave the gym, you want to create the optimal conditions for growth and maintenance," says Eric Sternlicht, PhD, president of Simply Fit Inc. in Orange, California. To promote recovery and help your muscles grow to their fullest, you need protein and carbs within an hour of finishing a workout, and, ideally, again a few hours after that. If you continually fail to feed your muscles after putting them through their paces, you'll end up breaking them down more than you build them up.

On the move

27 Never take the radiator cap off when your car is overheating. Leave it on for 30 minutes or so, or else you'll end up covered in boiling napalm-ish coolant. You can also purchase a special pressure-release radiator cap with a built-in safety valve.

28 Never take an airline seat that doesn't recline or is next to a rest room or galley, advises the Consumer Reports Travel Letter. When booking flights, make sure your seat is at least four rows' distance from both, and that it reclines.

29 Never book a connecting flight through a northern hub city in the winter. According to veteran travel journalist Laura Powell, you'll avoid the weather delays in the north by flying through southern cities.

30 Never try to negotiate a car purchase or lease in the late afternoon or evening, despite popular advice that suggests hitting 'em when they're tired and want to go home. Late in the day, salespeople will be worn-out - but edgy and less willing to deal, says Ashly Knapp of AutoAdvisor, which provides auto-buying advice and services to consumers (800-326-1976; www.autoadvisor.com).

31 Never buy a new-car extended warranty, says Knapp. The price of the warranty will probably be more than the cost of repairs over the first five years, and you're better off investing the money and using it only if something goes seriously wrong with your car.

32 Never travel abroad without mastering the local currency conversion rates, especially in countries where you don't speak the language well. Failure to do so puts you in danger of being ripped off - sometimes for a considerable amount - when a local merchant, cab driver or street vendor makes change for you.

In a job interview

33 Never allow a prospective employer to bring up salary requirements. "Preempt the issue if possible," suggests Marty Nemko, Oakland, California-based career coach and co-author of Cool Careers for Dummies. "About halfway into the interview, right after you've scored a winning point and they're envisioning you in the position, ask, 'What salary range have you budgeted for this position?'"

34 Never blast a former employer. "You have X number of minutes in an interview," says Nemko, "and you want to spend most of that time on the future, on what you're going to do for them. Stay away from the negative past because employers know there are two sides to every story. When possible, give short answers to hard questions and long answers to easy ones."

In a social situation

35 Never hold a glass in your right hand at a cocktail party. If your right hand is occupied, you won't be ready to shake hands with people you meet, advises image consultant Jennifer Maxwell Parkinson.

36 Never outdress yourself on a first date. If you're a T-shirt-and-jeans kind of guy, don't wear a suit and tie out to dinner, Parkinson cautions. Just be real from the start - that way, you won't have to keep projecting an image 'that isn't who you are.

37 Never leave more than two phone messages in a row. So, you think maybe she didn't get the first message? Think her answering machine might be broken? Think again, pally. She'll get back to you when she's good and ready, whether it's tomorrow, next week or never. Don't humiliate yourself by giving in to the temptation of trying her again. As far as she's concerned, you're out partying with Neve Campbell and haven't given her a single thought since you called her the first time.

38 Never go to a movie on a first date. You don't get to know each other - heck, you don't even get to look at her. And it's too soon to try out the old pretend-to-yawn-while-you-put-your-arm-around-her deal. Exception: really scary horror movies, which may make her snuggle up to you in fear. (OK, she's probably not really scared when she does this, but who's arguing?) We recommend anything starring Adam Sandler.

39 Never even try to answer the question, "Does this make me look fat?" If you say yes, you're in for it - but if you say no, she'll pick up on the split-second pause before you say it, and you'll still be in for it. The best you can do is laugh and say, "There's no way you're getting me to answer that." Hell, you're in for it anyway.