I've only ever laid down KK once.
That was in Pacific 25NL, where two short stacks both went all-in.
I called (About 1/3 of my stack), and a guy with about $50 went all in.
I thought about it for a bit, and folded.
Turned out I was up against 77, QQ, and AA from the large stack.
He got his payday, and I'm glad I didn't contribute to too much of it.