People who sit on the same machine or piece of equipment for an hour when it is the only one of those in the gym and manage only 3 sets. Other people (ie. me) might want to use that too dickhead!
Oh, and gym PT's who will organise a "personalised" training regime for you, only to see everyone who uses the same PT use the same "personalised" training session. I told this bloke that my knees are stuffed, and I have been told to take it easy so no weighted leg exercises. The bloke chucked in two leg exercises (leg press + squats with a kettle ball), and now wonders why I don't follow his exercise regime. Wanker.