My current pet peave-

Spin bikes - and other equipment and placement in classes - is first come first serve. Don't throw your towel or jacket over the bike to save it for your friend who is going to run in 10 minutes after the class starts. If someone is there before your friend, they deserve the bike/treadmill/step...whatever.
Don't save!!!!

Fortunately the end of the new years resolusionist period is coming closer and these people are starting to not frequent the gym as much. Just us hard cores left.