A person that sits in a bath tub and farts, and as the bubbles rise to the surface, he or she tries to catch them in his or her mouth.
by HLwakestud16 May 9, 2007
The act of catching a fart bubble in one's mouth, as it rises to the surface of the water in a bath tub.
Nat was fumgrunching last night.
by HLwakestud16 May 9, 2007