Face it, when someone is beating you by 17+ and the game is pretty much over, someone who won't grant you mercy is just being a jerk and just wants to rub it in on you. It might have been a good clean game and I just got my ass kicked, but I have no respect for anyone who denies the opportunity to just end the game and move on.
Anymore if somebody does this to me in a game that is already over, I just become a complete jerk. I run the playclock down to 1 if the clock isnt moving, I use my pauses and just try to make it as boring as possible for them. Sometimes I'll even just spike the ball on a random down and then run the clock down to 1 again. Haha, usually they just give me mercy after a few mins.