To try to have sex with a woman while she is sleeping. Usually this is done to a girlfriend or wife. Otherwise some of the more conservative people could profile this act as rape.
Guy 1: Hey man what are you doing?
Guy 2: Nothing just at my house and my girl is asleep and I really need to bust a nut.
Guy 1: I recommend you sneak one in.
Guy 2: Capital idea!
When somebody passes out and a person or persons take a crap and put it in the passed out persons underwear. Passed out person awakes and thinks they shit their own pants
Timmy passed out so all five of us gave him a SneakyPete. He thinks he was so wasted he pooped himself.
During a squash game, when oneplayer intentionally strikes another player with the ball, particularly with malicious intentions.
Pascal: "Hey jack, did you end up taking those growth hormones so you wouldn't be a pixie anymore?"
Jack: "SneakyTiki!"
(Jack proceeds to hit Pascal in the neck)
Fitzy: "You just freaky tiki'd the crap out of him......fooooty"