Pronounced as "foo-soo", not "fuh-soo"
When one clasps his or her hands together and thrusts them forward very hard at another's asshole. The result is a very sore anus.
Fusus are common in wrestling matches (in real wrestling, not the stuff on TV), when one opponent tries to grab the other, but misses, jamming his hand up the other opponent's ass.
Jim: The bastard was doing push-ups, so it went up behind him and gave him a fucking fusu!
Darrel Fitzgerald: Damn, my asshole sure is sore from that fusu I recieved in that wresting match yesterday!