Grunting. It seriously unsettles me, although at times makes me giggle.
Dropping weights. Terrifies me. If you've been nlifting all this time, then spend that last one pulling it down.
Girls (or guys, although mainly girls) doing ridiculously low weights. I know we all have to start somewhere, but I was pretty poor when I started and I didn't do that low!
People (mainly girls again) on their phone constantly. If you can text/be on the phone whilst working out, you are not working out properly.
People walking on a steep incline on the treadmills. Does that actually do anything?
3-4 guys surrounding a machine which has 2 or 3 seats. And staying there for around 20 minutes. Rotate round 1 seat maybe? I undeerstand gym buddies but 4?? Seriously?! Also very unsettling for me (a girl) to walk over and start using it, if you're standing right next to me.
People who talk to me in the gym. I understand things like 'you using this machine?', 'can I grab this?' etc. But please don't start a conversation with me in the middle of a workout. Do I look like I'm able to reply?