Rump People

The Rump People (or Butt Heads) make an appearance in the episode "Freak City." They are thrown into panic when their village caught on fire, possibly due to Gork 's lava breathing. Finn is persuaded by Jake  to help the village but when he arrived he realized he hasn't learned how to use his new foot body and falls on a small flame. A few villagers see him and label him a freak, they then proceed to throw him under the bridge with the rest of the "Freaks." They are not seen for the remainder of the episode, except for the babies that Jake saves. On Pen Ward's Formspring, someone asked what the Freak City villagers were supposed to be, Pen replied: "Butt Heads."

Appearance
Their heads are shaped like butts, hence their names, Rump People. The Rump People hate the Freaks, which include Gorflax, Gork, Kim, Trudy, Wee Wee, Zap, Finn, and possibly Jake. Every time they see one, they throw them under a bridge, known as Freak City.

Trivia

 * Because of their shape and colour, many viewers mistook them for teeth.