I think I'm one of maybe a dozen people at the Bally's I go to that actually re-racks plates correctly. As far as dumbbells go...don't even bother. Even the staff leaves them out of order. So I'm basically used to both of these things happening, and thus neither of them really upsets me. Besides, it's a mini-workout just taking off all the weight that the guy before you had on there. Heh.
What I hate more than ANYTHING is people who don't wipe down equipment after they finish using it. And it always seems to be the guys that sweat a LOT who don't do this. It's disgusting. I won't even use my own towel to clean it up; I'll go grab some paper napkins to wipe that nasty sh!et off.
And yes, I too dislike it when someone takes the only piece of equipment in the gym for a particular exercise, does one set, and proceeds to talk on the phone or to his friend for 15 minutes. You want to talk at the gym? Fine, but move your towel off of the machine so people can work in with you.
I've yet to have anyone turn me down when I asked them for a spot or to work in, though. But what I do dislike (even though I'm grateful for their attempting at helping me) is when someone over-spots you. Ya know, you'll be on rep number 3/10, and the guy is practically lifting the entire thing for you. Please, please, PLEASE don't touch the weight unless it looks like I'm gonna kill myself. Thanks.
As far as proper form goes: if someone wants to throw on 30lbs more than they can do, it's fine with me. Just don't go and lecture ME about how MY form should be. Just because you only have a 3" range of motion in the military press doesn't mean everyone else should workout the same way.