unfortunately i can admit to having done something similar, though not proud of it. it was 'if there is a defence' on the back of a ton of verbal from bowler and fielders while trying to keep us in a game, there was not scrap just a reminder that if i was as bad as he said i was that he should go fetch the ball from the gardens and get me out with it - though the language may not have been quite so pleasant. few words each way exchanged and a few overs later we both shook hands and apologized, not going to be best mates but we were both in the wrong.
note: im slow, fat, and not very good so i would have gotten out eventually - all they did was make me try harder
not saying i was in the right, and im certain that the subject of the topic should expect a bit - assuming he was unprovoked of course
are we saying that sledging is only acceptable if its the fielding side though? im not saying abuse, but a gentle chirp doesnt harm anyone and if it puts the bowler of his length and distracts the fielders why not? its no different to whats coming back.