Dry or semi-dry vaginal discharge often found in the gusset of women's underwear. Usually a yellow-white color with a similar texture to mashed banana. See Gusset Fudge.
While all alone, John went down his friend's sister's laundry for her soiled grundies, delighted to find some fresh banana mush.
The act of taking a banana in a sauna, unpeeling it, mashing and smearing it into the hairy sweaty back of a gross man, up and down. And proceeding to lick it off, or scrape it off with your teeth, and swallowing. And repeat several times.
"Would you rather do Banana Mush or jump off a cliff?" "Jump off a cliff!"