The extreme version of Muffin Top. So extreme the top half grows from the head down then abruptly stops at the hips( like a mushroom ) to reveal thinner, and possibly even nice legs. Gravitational wise.. we don't know how this is possible. But many have proved gravity wrong by this odd shaped silhouette. Also known as Toad Stool.
"Wow, she has nice legs considering what her top half looks like."
"I know, she has a mushroom top, that's why she wears short skirts and then baggy sweatshirts."
Term used when a guy does a girl thats so young all he can get in is his mushroom tip(aka his dick head). You have to be really desperate or really sick or both to want this to happen.
Joe you would mushroom stab her? Thats just wrong dude theres not even any grass on the fairway.