I was pretty sure I recall seeing Nadal do it once but seems I was wrong. My bad. Nevertheless he has defended it's legitimate use:
“If you do it with the goal to improve your game, or like a tactical thing, I support 100 per cent,” said Nadal. “If you do for disrespect the opponent, is not a good thing.
“Everybody knows internally if you are doing in a good way or in a bad way. For me is no discussion about that. Is part of the rules, you can do it 100 per cent. Is about yourself, if you feel good doing or not. Depends.”
I don't think Murray intended to disrespect his opponent. He was using it tactically against a very difficult opponent.
Well, for one thing, Murray is no longer at the level of an elite player. He is an injured player struggling to become competitive again after undergoing radical hip surgery. But trying to compare hitting an unorthodox serve with leaving the court and not actually playing is just utterly ludicrous. No comparison whatsoever!!