A butt belonging to the community as opposed to a butt belonging to a single person. For example, those with questionable morals may have a butt belonging to a group of people or the community as a whole.
Jeremy: "I don't want a girl with a community butt."
Kyle: "I understand. You want a privately-owned butt."
A combination of "gross" and "grody." Most likely said when a person is flustered by an overwhelming characteristic of another party. Upon trying to insult said party, the first person combines the words and becomes more flustered.
Jeremy: You're grossy.
Kyle: I'm not grossy! You're grossy! I don't even know what that means!
Jeremy: It's like gross and grody. Duh.