5. Not putting weight plates back
Most gyms have a policy about this one, but few follow it. If you are using a barbell or a leg press machine, be sure to remove the weights you’ve used. Most people do not want to have their workout consist of putting weight plates
back and find this highly annoying. I've have seen the leg press machine with 800 pounds of plates left on it. Removing most of that is a workout in itself!