When your cum is thick and yellow like mustard.
I had to piss so bad but Lauren wouldn't stop with the head! so when i came all over her face it was mustard nut.
by Chuck Bucket March 01, 2005
On hot days your ass and nuts start sweating, and some of your butt sauce begins migrating to your nutsack across your taint, causing irritation and general discomfort
I had serious mustard nuts yesterday while mowing the lawn.
by MonkeyMan1140 May 03, 2009