Post-flop, there are many situations to fold them. It is JUST one pair, usually with little prospect of improving.
Pre-flop, there are 2 clear situations I can think of when they should be folded(and I have folded them):
(1) In a satelite, you have enough chips to get a ticket, but if you lose even some of your chips, you would not have enugh chips left to get there. AA will win a showdown 90% against a single random hand. Why take the 10% unnecessary risk of busting just out of the prize when it is 100% certain you will get it by NOT PLAYING?
I have seen many players play
hands much worse than AA in such situations, when they should be folding everything.
(2) A similar situation arises when the prize structure has wide steps(many places pay the same prize before the next step). If the stack is very short and close to the bubble for that step, it might be correct to fold AA if doubling up will do very little to propell you through the next prize level. This situation requires more judgment based on the specific prizes, blinds levels, etc.
Finally, Sklansky describes a situation when ANY hand(including AA) should be folded at a major bubble when you are the chip leader. If one of the small stacks goes all-in, then it is best to fold any hand, because if you win, you lose the profitable situation of stealing blinds from small and medium stacks. The gain of winning one hands is small compared to the gain of stealing with impunity and increasing a big stack.
I disagree with one of the posts where it was said that no pro would ever fold AA pre-flop. There are clear situations when AA should be folded even pre-flop.