if he's being obnoxious and aggressive like following you around and chastising you, file a complaint. otherwise, look at him, say "duly noted" and continue on. pull a honey badger on that shit and ignore him. you really have to sincerely not give a flying fuck about what anyone in the gym thinks, says, or does. depending on the gym, 90% of the people you run into wont know their ass from a hole in the ground. unsolicited form advice is the fucking worst, especially when its coming from bros about squats/deadlifts. that being said, you've been complaining about your squat form for awhile now, so seriously, post a video of it.