The only time I'd ever fold KK preflop would be if I had an indication of some sort that my opponent had AA. I usually use their betting pattern in the current hand versus their previous betting patterns.

For example, if they've been betting pretty tame and all of a sudden it's super aggressive raising preflop, I'd suspect they have pocket Aces. The big problem here is that when I have KK and I suspect they have pocket Aces, I still call because I REALLY want to know if I'm right.