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."
Their heads are shaped like butts, hence their name, 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 it under a bridge, an area that becomes known as Freak City.