In the gym, as in life, there are do's and don'ts.

Some are obvious. Don't go to the gym with your wife, then ogle the hottie next to her. Don't spit in the water fountain. Don't urinate in the shower like George Costanza on "Seinfeld." These are a few examples of bad gym behavior cited by trainers and fitness center managers when asked for examples of how not to behave while working out. But in other cases, the line between good and bad gym etiquette might not be so obvious. Let's hear from the experts:

Noise

"I had a lady in my Pilates class talking on her cell phone. Her assistant was also in the class, and she was talking on her cell phone!" says Washington, D.C., Pilates instructor Chauna Bryant.

"I was really upset. I said to them, 'Is everything OK?' and they both put their phones down and looked at me like I was out of line."

Even gyms that don't have bans on cell phones in workout areas often prohibit them in locker rooms out of privacy concerns. "It seems every phone has a camera," says Dick Snyder, owner of Life-Sport Fitness in Philadelphia.

Blasting a TV at top volume when headphones aren't available is inconsiderate. So is cranking up your iPod.

Sometimes weightlifting leads to loud grunting, which some gyms discourage, or prohibit. At the Planet Fitness national chain, noisy members are given a warning. But when a client grunts, groans or drops weights a second time, managers can set off an actual alarm.

"It's called the lunk alarm, and it's a blue flashing light, and sounds like an air-raid siren," says Glenn Stuart, general manager of the Planet Fitness in Meriden, Conn.

Hygiene

"The main thing that bugs me is when people show up sick. You infect everybody else," says Melody Schoenfeld, owner of Flawless Fitness in Pasadena, Calif.

And there's the basic issue of cleanliness. "I actually turned down a client (for training) because he had on a knee brace he hadn't washed in a year. He smelled so bad. ... Use common sense. Take a shower," says Schoenfeld.

"Make sure you wipe the machines off. A lot of times people leave them all sweaty and gross," says Bryant.

Dr. Douglas Robins of the Florida Society of Dermatology & Dermatologic Surgery, says sit on a towel in a shower/sauna, never share towels and cover cuts or scrapes to avoid infections.

Common courtesy

"People should not wear loose, wide-leg shorts. You can see all their business," says Bryant.

Underwear and support garments are a must, says Schoenfeld. Another pet peeve of hers? "People who try to correct your form -- unless you've asked for their help."

And "do not hit on the hot girl on the treadmill," advises Bryant. "She's working out! If someone is getting a good sweat on, leave them alone."