Men flirt, even when they don’t really mean to. It’s a natural reaction to being around a woman. In some instances, men are just being nice. It’s got nothing to do with physical attraction. There are just some cases, and kill us for it, we’re nice to the opposite sex for no reason. Your jealous girlfriend views every nice gesture as flirting.

Why It's Harmful: Just as you can’t mention another woman around her for the rest of your life, you can’t be nice to another woman, either. Every woman you encounter together -- from the friendly waitress to the helpful desk clerk -- you’ll have to treat  with very little kindness or be accused of trying to get into their pants.