A puckered asshole or anus. Given the name due to the similar look of said asshole/anus to a balloon's knot covered in rust.
Dude 1: Did you ever fuck that one bitch?
Dude 2: Nah bro, I was only able to tongue punch her rusty balloon knot.
Dude 2: Nah bro, I was only able to tongue punch her rusty balloon knot.
by Helvetesturm October 21, 2013
Get the rusty balloon knotmug.