when giving a man head he often will cry out "Oh I'm gonna cum!" The you brace yourself for the sexual eruption... except as he cums he pushes your head down causing your throat to close and the jiz to come out of your nose rather than be swallowed.
(kinda like when milk comes out of your nose from laughing in the cafeteria)
Damnn! my girl was sucking on my penis, then as i was cummin, i made her deep throat my junk and... Shit!!! I cafeteria'd that ass!!!!!!