Best definition
A very fat girl with a yeast infection.

Ted: Check out that girl over there…She’s smiling at you. You should go talk to her.

Bill: No way! She looks like a yeastopotamus.

David Attenborough- famous Nat. Geo. narrator: “In the wilds of Africa, the only creature that scares the mighty cockodile is the equally large and ferocious yeastopotamus.