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
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