The act of fellatio performed on a man who is having a bowl movement on the toilet. iow, giving head to a guy while he's taking a huge dump.

Referenced briefly in the american pie: beta house movie, wherein a test to join a fraternity includes the requirement of receiving said carnal pleasure.

could possibly refer to the act performed on a woman, but the logistics are much more complicated
"Yo, your mom gave me some grundleingus last night."

"Dude, thats gross."

"no, what's gross is that i had just eaten some taco bell"
by _lou_ July 10, 2008

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