Well, I'm late getting my $0.02 in this topic......
I don't DA and tell everyone who challenges me to DA just that "I don't DA". Reason? because 99.89% of those making the challenge are POed that they got greased by a mediocre player and need to redeem their "superior" pee-lot status. I will readily acknowledge that it was not my prowess as a pee-lot that allowed me set them up and shoot them down, just that i was able to capitalize on a mistake on their part. I feel that if I DA'ed with a POed pee-lot, I'd gain nothing to add to my skills set.
All of that said, i have contradicted myself a few times over the years of playing AH (like 3 or 4 times) by going to the DA with someone that I recently shot down in the game, and it was not because they raged at me either but because I felt that I could learn something from them and them approached the whole DA matter as an adult vice as tantrum-throwing child.