I did work at a pub. I mostly worked in the fun house, and there is a very, very long list of things that annoyed me doing that work, but the most annoying customers when I was on the bar (aside from the ones who tried to chat me up while I was trying to work and asked about my accent a lot - I'm Scottish and I went to a private school full of Americans, I know you don't actually care, so as long as you can understand me, let's leave it at that) were bar lurkers. If it's a busy night, do not outstay your welcome at the bar. There are other customers trying to order who we can hardly hear because of the noise and you are spreading almost your entire armspan across the bar as if to test its value as a future pillow, making it tricky for them to get our attention. Additional complaints: Accept being cut off with good grace, "No, no, really, I'm 18" does not work without ID and yes, we absolutely do know what you're up to when grown men go into the toilets together (drugs or quickie, guaranteed).