When a man shoves his dick down a chicks throat, and right at the point of deepest penetration, busts. This in effect causes the chick to vomit up the dick (note, the chick does not simply vomit, she specifically vomits the dick out of her throat) causing the most splendid sensation for the man.
Jackson: Yo man did you have fun last night with that one bitch?
Guilhem: Yee son she gulched my dick so hard i still have gulch juice up in my pubes.
Jackson: Niiiiiice, gulching feels fucking bomb!
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).