look up any word, like fleek:
 
1.
A complete letdown. Something you don't want.
Yeah man, my summer is a total underfuck.

Our fuck was a total underfuck.
by Ownthink June 29, 2005
 
2.
The act of making love to someone in an unsatisfactory way.
She complains I was just another underfuck.
by Frank1957 October 17, 2007