There are some things that are minor irritations, like people being inconsiderate with equipment (curling in the squat rack, leaving weights lying around etc.) and being very loud and arrogant in groups. The one thing that truly annoys me, though, is people giving bad advice. I suppose they mean well, but when you hear a clueless newbie getting advised by an equally clueless but more experienced guy, it's frustrating, particularly if they're advising on lifts where bad form is likely to be dangerous. I sometimes have to restrain myself from intervening as I'd likely end up doing more harm than good and probably wouldn't be listened to over big-armed, chicken-legged guys.