In the first few weeks they tried to convince him with polite conversation, arguments, logic, kindness, anger etc, but he is so thick-skinned (and just thick) that they have given up.
Just imagine....
If you're in a room and there's someone shouting, getting drunk and throwing food around, arguing with people, and nothing you or anyone can do has any positive effect on him then you DO find the atmophere is low for everyone but the trouble maker.
They are over the shock and resigned.
He is a selfish knob and ruined their time in there.
He thinks he's wonderful but hes NOT.