The act of taking your dick out of a chick's vagina and finding that she shed her nasty pubes on you, and there are crabs running around that look like little cats.
You immediately lose your stiffy, and it slumps there in semi-boner mode-- thus looking like a cat's leg hanging from your southern region.
John: Bro, it was a nice f*ck, but I got a nasty little foreign surprise.