a) when a reference to 'muff' is made during conversation. This is called "dropping the muff-bomb"
b) Having the same meaning as a "Fanny Fart" or "Tawt" the releasing of air from woman's vaginal cavity.
Friend 2 - "nah man, not yet... Will catch it after I see the girlfriend, maybe go with her?"
Friend 1 "oh yeah? you gonna go touch the muff are ya?"
Friend 3 - OH what?! - do I smell a Muff-Bomb?"