Well the guy is obviously pissed with himself on losing... just take the proferred pieces and sail onwards to your win. He could probably have made your life much harder...
No need to sympathize with the loser, but no need to trouble the loser further too.
BTW a notable example for a player who does this in OTB tournament practice is no other than Vassily Ivanchuk. I also do from time to time..
How would you feel when you're in a winning position, your opponent starts playing suicide chess, giving away his pawns and pieces? I think this is very unsportsmanlike. He could just resign. No need to congratulate the winner but no need to annoy the winner too.