Probably the biggest things that irritates me is the social club people, or the high-schooler crowd. I cannot stand when there are literally 15-20 people standing in the machine, or free-weight area DOING NOTHING, but talking, and hitting on the hot gym girls. Get the hell out of my way so I can move some weight if you aren't going to. They mess up my set rest times, and then randomly move onto machines/benches to sit down while I'm trying to move weight.
Glad my gym has a juice/shake bar, so I'm luck not to have to deal with social club on the lifting floor. Just the 5 fucking high school kids all on bench.together.
I really don't mind a little conversation on the floor at all, but can't stand the guys talking accross 2 machines or loud enough for everyone to hear. Usually the same guys talking about how fucked up they were the other night, and how much they are going to drink tonight, while they are lifting.
Funny thing is my gym also has a juice bar, a pretty big one, I do agree a little talking is fine by me, but when they are all standing there for over 10 minutes talking that's where I start getting irritated.