Jack, why is calling the worst thing he can do here?

My thinking would be, re-raising will probably get everyone except AA to fold, but AA will re-raise again. So, if you're ahead, the hand ends now, if you're behind, you'll proabably have to call or fold to an all-in. Villian has a full 100bb stack, so I don't want all of that in yet.

I'm not 100% convinced we're behind here, so I don't like folding.

That leaves calling. I'd consider calling with any pocket pair for set value here, that certainly includes KK.
You've got position post-flop, so my advice is to call, and play the flop. But I'm still playing below this level, so if my thinking is wrong-headed, let me know.

When I've got AA, I love it when villian can't seem to find the fold or call button.