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1.
Urban legend on UW Eau Claire Campus. Sightings are likened to seeing Big Foot. Known for breaking girls pelvises. Drinks entire kegs by self.
"Dude there was a Mouseballs sighting today."
by StankCity April 24, 2010
 
2.
slang for damn. usually used as an exclamation to a blunder or mistake.
you dropped mom's precious vase? aw MOUSE BALLS!!!
by Ratbiker May 23, 2007