If you think back to the infamous Clattenburg derby, Moyes laid into him afterwards, and was immediately slapped with an FA charge.
It was quietly dropped and neither the FA nor Everton/Moyes mentioned it again. Makes you wonder why.
A few years ago I met a former Premier League ref at an event. Asked him about Clattenburg and he said he hadn't seen that game, but did mention that when he was a ref, they had Clive Thomas come in to give them a motivational talk. He said he was a bad tit - said that whenever he reffed and got an assessors report, he binned it without reading it as no-one in the stands was qualified to judge him.
This was before the days of professional referees - the guy I met quit reffing to focus on his career.