Definitions by Gigii

USI 

Unidentified Sex Injury
Those bruises, cuts, muscle strains, and torn ligaments that happen after a night of vigorous sex - and you cannot remember exactly what you did to cause it.

"Holy crap! My one leg is completely covered in bruises, but I don't remember what we were doing and how it got that way!"

"Dude, that is a serious USI."

USI by Gigii June 22, 2008