people who use a machine, claim they are 'resting between sets' so you cant use it, then they walk off.
people who try to show off what they can do, especially when what they are doing isnt very impressive
people who do one rep on each machine then get angry with people for using certain machines for too long
people who do actually spend too long on machines (eg. 10 minutes trying to do one rep. If you cant do in the first 30 seconds, you cant do it. move on.)