Grundel is another word for chad: the region between the balls and the arse-hole; can be an erogenous zone for some.
Girl: I was fingering that part between his balls and his arse and there was shit there.
Everyone listening remained silent but later laughed among themselves:
'Eww! He had a shitty chad.'
When you measure your dick, you don't start at the arse-hole and include the chad; you risk getting shit on your measuring tape.
The Grundel Grab is a sexual technique attempted by women who read too much Cosmo magazine. This maneuver which involves the prodding of the male sexual partners grundel, will in theory bring him to climax as this is his proposed G-Spot.
The validity of this theory and technique are both questionable due to a lack of substantial scientific and/or medical evidence.
Although rarely attempted, if done without warning, the male partner may resort to violence in order to protect this sacred and noble region, often referred to as "no mans land".