The flap of skin, in males, between the scrotum and the anus, which can be used for various things such as clipping flashing lights to. Grundlesac's can vary in size from droopy to so small that they can barely be noticed.
Damn Alex, that is so sweet how you can clip that pulsing belly button ring to your giant grundlesac.
by pdiddy July 12, 2004
by PDiddy January 28, 2015
verb-meaning to have intercourse with a person whom has lost all bodily control and conciousness, laying like a dead fish.
When I was in college, I enjoyed the occasional dead fish at frat parties, thanks to our good friend ruffies.
by PDiddy October 27, 2004
by Pdiddy April 30, 2003