Upon seeing a chick so hot, you instantaneously cream your pants. It's like a super-fast wet dream, but awake and in public. Often used in hyperbole since guys don't actually do this, except lame-ass premies.
Guy: Dude, did you see how tight that chick's ass was?
When women and male feminists genitals get instantly lubricated by precum or lady juice the moment they are excited by something i.e. 50 Shades of Gray, One Direction, Feminist Frequency.
John: Oh did you see they're making a cross over of Fifty Shades of Gray and 12 Years A slave?
Peter: Yeah I saw the lead actor will be some coked up nigger into bondage with white women.
John: I heard Scott in accountings wife got INSTAMOIST because she has a thing for black men, I hear Scotts a bit of a cuck.