The thing is, it happens to everyone. You only have grounds to bitch and complain if you had your backpack and towel sitting on the bench and someone moved them to take your space. Clearly, in that case, someone was using the bench. Going for water and then bitching about the age of some guy who took your bar clamp makes no sense. Why would anyone think he KNEW it was being used? Going and taking the clamp back without any explanations is what sounds childish.
I heard one older man almost yelling at a girl who was sitting at another bench because he asked to work in with her and she said she only had one more set. It seems like some people, especially newbies, young or old, have no clue about gym etiquette. Yell at a girl? A cute one? Who was actually training hard and looked good while doing it? Dumbass.
Doing curls 3 inches from the dumbbell rack in front of the mirror as if no one else will be needing any dumbbells today is stupid. Yet I see many do this on a regular basis as if they don't understand the concept.
Jumping in front of the mirror to do your exercise when someone behind you may have been using the same mirror to monitor their form is retarded.
Taking someone's dumbbells when they have a towel on the machine, bench, or rack is stupid unless they have been gone for longer than 3-5 minutes.
There are tons more but it seems most don't even know these.