Boobs that are freakishly large or just awkward in shape. May look like two clown shoes stuffed in a bra or two carnies stuffed in a bra. Usually the girl with the clowntits thinks she has the best boobs in the world and puts them out there for everyone to see.
Stacey: Oh my God, look at that girl's boobs!
Lacey: Oh my God I know. What's wrong with them?
Stacey: They're clowntits.