Based on the Kate Hudson movie Skeleton Key, in which an old lady steals her youth, skeleton keying is when you and your friend are both deservedly hungover, and suddenly one friend begins to feel much better, and the other friend much worse. The friend that is feeling better is 'skeleton keying' the other, or stealing their essence.
Alex, a minute ago I was fine, now I can't get off of the floor, and you're suggesting we walk to McDonalds? How are you feeling better, are you skeleton keying me?
I need to take my girlfriend to the pharmacy to buy Advil because I skeleton keyed her... but first I need to wash my finger. While I'm there, I'd better buy lubricant for next time.
By Aimil
Skeleton Key
When a person is having sex with someone doggy style, and sticks their ring finger into the person being fucked's asshole, then turning their finger like a key