As rating increases, players definitely do not get more polite. Almost the opposite, so I've found!
Live chat 'banter'
I have to say that I do run into this from time to time. I would either let it go or disable chat. I don't know about you, but I prefer not to chat while I'm playing anyway, it decreases my concentration on the game.

If I win, I'm a cheater. If I lose, I'm an abomination to the human race.
You can't go wrong with this kind of encouragement!
Moral of the story: Laugh or disable chat
I would just disable chat with this opponent. Note who the opponent is. Then, next time you play them if they are abusive again, report them.
I don't mind losing - it's part of learning. Why do so many opponents in live chess see fit to give me grief if I make a mistake or am in a losing position?
I don't really give a hoot, about the nature of the comments, but some of the people on here deserve a 'red card' for unbecoming conduct.
You should lose rating points for being downright cheeky and rude. No need, esp from players with a decent rating >1300+.