I guess I have been very luck so far and have not experienced this.

I haven't had it either, but i imagine in correspondence games this is very frustrating.

Maybe they are not bad sports, but they are thinking more critically now that they are losing. If you are winning, then your game is moving forward as planned. If you begin to lose, it requires a reevaluation of that specific game, and would show that more critical analysis is required for the following moves. I give people the benefit of the doubt, and just load up on more games when mine begin to wane. I think this type of action that you describe is something that I should do more often, as I have made blunders by moving too quickly all too often.

I think that we sometimes misunderstand the motives of unhappy players. 

Could it be possible that it takes them so long to move when they are playing poorly because of the massive brain trauma that they incurred upon having made the move that created their downfall? 

Could it be that the cause of the poor playing is a result of what is causing them to take longer to make moves (nagging wife for example)?

Before we assume that they are punishing us for their mistakes, we should make sure that the reason for the slow playing isn't caused by some other reason (maybe their dog keeps on biting their hand when they try to make a move and therefore have to wait when the dog is either eating, sleeping, or dead).

FAIR ENOUGH !

Thanks for all the comments.

I guess patience is the key then.

CHERRS.

In this case, sportsmanship isn't relative. Sportsmanship doesn't have much to do with the rules, either. You can follow the rules and still behave poorly. Unfortunately, the anonymity provided by the internet protects your opponent's right to act in a petty manner. Just make sure you aren't behaving this way yourself.

 And you should resign that game

I always loose with grace & style

Yes, sometimes this happens in CC games. Well, we should make our moves and win.