Currently I play a game and one sore loser (I beat him before) told me openly in the Chat he is not in the Game to win it, he just wants to make sure I will lose the Game. Poor fella, I would pay him a psychological therapy if I'd know his real name - he really needs it.
Also I could not avoid the impression that if you decide to rematch a game in which you won, some players tend to be very alert if you are again competitive.
How about your experiences?
Do you generally avoid playing old enemies?