#5 Re-rack the dumbbells/barbell after using it
Re-racking the dumbbells is something you must abide by. Once you have finished using the dumbbell/barbell, do not dump them on the floor, place them back in their respective racks.
This at least makes the gym look less messy and the other plus is that you burn little more calories while walking with the dumbbell/barbell back to their respective racks.
Hence, the fifth etiquette is to re-rack the dumbbells /barbell.
Also read, Know the critical concept of "Maintenance Calories" for weight loss
#6 Stop screaming in the gym
This is especially for men who scream while lifting heavy weights in the gym and is another irritating thing to encounter for others in the gym.
Avoid screaming, instead, focus your breathing and technique which will reap more benefits and again lift weights which not your ego but you can realistically handle.