Dunno what it's like in the US, but here in Australia; When the footy season finishes and every one of them packs the freeweights area spending 2/3 their time talking and hogging benches, getting 'shredded' for Stereo/Future and act all weird when the gym manager kindly tells them to start lifting or get out.
When some sped turns the fan off because they "dont like the noise" despite the fact you're in the zone halfway through a 1 hour cardio sesh and you want to be able to feel some air movement.
That guy who always has to butt in on your workout because your form isn't 100% right. I appreciated the dude when i first started lifting who told me to "stop squatting because i'd hurt myself, and go see a PT and get my form corrected" and then returned to his workout. I don't appreciate some mid-twenties dropkick telling me the finer points of bicep curls simply because he "learnt it better from my mate who is like seriously an a-grade shredded comp lifter with like a 2% bodyfat bro"
That guy who always seems to be doing the same workout as you, even though you SWORE he was doing chest like 2 seconds ago he's suddenly jumping on the low rower with you...
Chicks who give you dirty looks because you dared to glance in their direction. Yes, you're at a public gym, people will look at you including males. I look at dudes too, i look at the mid-fifties lady on the walker, i look at myself in the mirror, i look at the roof. My eye is drawn to movement as i am an invertebrate and that is is the nature of eyesight, and you walked in front of me. I have 0 interest in your stanky wide-footed box-gap.