when someone/something does something sneakily to fuck up your day or plans - usually friends doing it to prank you, but can be otherwise.
In Halo, when someone assassinates you from behind - they are a sneak fuck... especially when said person is on your team.
by ashpagrass December 21, 2010
When someone jumps behind you and scares the crap out of you in a most vulgar manner, mostly thrusting their crotch at your behind. The attacker usually screams the words “Surprise Butt Sex”.
by the nig thumper September 30, 2011