First of all, that is the proper technique on bench if you're lifting for pure health reasons so you can’t really knock him for lifting that way. When you go past parallel it causes your ACJ to separate. This injury is even nicknamed “weight lifters shoulder”. So I can’t knock him if he’s doing it to prevent injury but at the same time he is full of shit if he claims that as his max. It’s not a full rep so it is definitely not a true max. I don’t use this technique but I have other goals.
As far as cheating goes why would anyone be upset with someone for cheating on curls? If anything I would be upset with someone who doesn’t cheat (especially if you lift by yourself). Everyone knows you reach positive failure before negative and the only way you can come close to negative while lifting alone is to cheat it back up for some good negative reps. I love a couple of cheat reps at the end of my curl sets.
A couple of legit “pet peeves” I saw mentioned were 1) When the spotter keeps continuous contact with the bar. Hell, there is no way you can gauge any kind of improvement because it is impossible to tell how much of the weight you are lifting. The slightest touch can make a huge difference. 2) When someone squatting humps the air and calls it a rep. The thing about any lift is you are more injury prone if you do not reach the point where the lever of the lift is parallel to the ground or if you go too far beyond this point. This is even truer with squats.
To be totally honest I usually don't give a shit what anyone else is doing or looks like, although occasionally I might think to myself “what a fuckin’ ass clown!” Normally if someone asks or if there’s a young kid just doing something completely wrong I will give them advice but other than that I mind my own.