Monkey Mustard is when you fart so hard you shoot out globs of shit. Similar to shart.
Becky: -LOUD AGGRESIVE FART- (also sounds bubbly, and sounds like when you squish flarp.) Keisha: OOoo girl you definitely just shot out some monkey mustard.
When you push a fart, and eventually shit at the same time creating a shart. (Originating from a family in Ohio)
Ava: -bubbly fart- . Steve: Did you just shart?