People who don't practice movie theater etiquette.
I took my mom to see Infinity War and there was a whole row of young teens talking THE WHOLE GOD DAMN MOVIE. Multiple people, including myself, told them to shut up and they didn't care at all. Unfortunately this was Israel, so the staff didn't care much either.
But it happens in America too. People talking through out the movie, being on their phones, etc. BURN!
I once had a dude take selfies of himself watching the movie (with a straight face) the whole movie.
WITH THE GOD DAMN FLASH!