I stopped working out at the gym a while ago and built a home gym in my basement because I didn't want to deal with the annoyances. It's worked out good for me.
There are just always a lot of jerks at any gym.
But I never really let what people did bother me unless it directly affected me. All to often it did, like many of the incidents mentioned already. Still, why should I care if someone I don't know is doing some stupid shit, as long as I'm not personally affected?
People do dumb and potentially annoying things all the time and not just at the gym. My philosophy was always: I came in here in a good mood. Why should I let you change that? Give you power over me?
Course, if I was already in a bad mood, that's a different story...