The only thing that really annoys me if is someone is somehow preventing me doing my workout. For instance by hogging equipment.
Now, if that person is, say, using lots of weight for a big deadlift, that is entirely forgiveable. If someone however is – to pick random examples – using a bench press for bench dips or as a stool to sit on in between sets of starjumps then I have less sympathy. Likewise people who use the squat rack for their curls, people who hog all the dumbbells and hardly seem to use any, and people who load up all the weight they possibly can on plate-loaded machines, all in the positions which give them the most leverage. They might as well use half the weight less dickishly placed but that wouldn't look as hardcore. They use **** all range of motion as well.
Also people who just take weights from me without asking me if I'm using them. Yes I damn well was! Sneaky bastards do it while I'm distracted.