Don't use your towel to dry the sweat from your face and then put it on the leather.
Say "thank you" to other guys who open a door for you.
don't try to figure out who is the owner of a thingy in the gym someone lost. bring it directly to the desk
make sure the weights are fixed well on the bar and don't take too much weights so you are a risk for others beside you
Dont grunt and groan unless your getting a BJ, or you have 500lbs on the bar.
Dont sit on your phone between sets, taking 45 to do one body part hogging the bench
Dont spit in the water fountain, that just gross