The No-Brainers

Let's get the basics out of the way real quick so we can move on:

Flexing/posing in the mirror. Even if you've got the goods, there's no reason for even the smallest pec-squeeze directed toward the gym mirror. It screams out one of two things: "I'm sooo in love with me", or "I'm so insecure I could almost pee in my Joe Boxers." Yes, flexing brings out muscle striations, but if you're not 3% bodyfat and getting ready for a contest, you can save that shit for home. Even then you don't need a mirror; that's just egotistic douchebaggery.

Dancing in the mirror. Save it for your floor-length bedroom mirror next to your Jersey Shore poster.

Shadow boxing. If you're not in a boxing gym or a dojo, nobody's going to think you're anything but a poser d-bag. Which you are.

Grunting. There's the grunting that comes with extreme physical effort, and there's grunting to get everyone to look at you. Anyone who's been to the gym twice can tell the difference. The diabolical problem with d-bag grunting is that it's self-re-enforcing. This is due to the sad but undeniable fact that a douchebag is incapable of discerning the difference between a look of admiration and a look of "haha, what a douche." The result is the saddest bit of logical thought you're likely to find: "I grunt when I lift. People around me look on in admiration. I'll grunt louder." Douche. Moving on.