brown mushroom 

After a prolonged bout of anal sex, the giving party turns the recieving party around and proceeds to thwack them on the forehead with their penis/dildo leaving a brown mushroom in its stead. Also known as the brown mushroom to go, because one does not want to stick around after giving a brown mushroom.
notes: brown mushroom is only theoretical, poo does not actually stick to the penis in quantities that would make this act possible.

Johnny gave Jenny a brown mushrrom...to go.

brown mushroom by [e-mail] October 5, 2004

Brown mushroom tattoo 

When you fuck a girl in the ass then slap her in the face with your cock.

I was fucknig your mom in the ass then pulled out for a second and gave her a Brown mushroom tattoo then kept on fucking.

Brown mushroom tattoo by chaigh October 22, 2008

little brown mushroom

When you release your load from your butt

I had a good little brown mushroom

little brown mushroom by Ethan Croke December 14, 2016