grundleingus 

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"

grundleingus by _lou_ June 20, 2008

grundlelingus 

the act of licking a grundle

Ben, a grundle connoisseur, expertly gave grundlelingus to Eric's expectingly sweaty and hairy grundle

grundlelingus by jdubbs January 26, 2006

grundlingus 

The high art form of making sweet passionate tounge love to the space between a man's balls and anus. Similar to its female counterpart, cunnulingus.

Guy: Man, what happened last night?

Dude: We got wasted last night, and then Michelle gave me some serious grundlingus!

Guy: Hell yeah!!!

grundlingus by AaronTimothy November 8, 2005