Closet Muppet

A slightly less charismatic, less attractive muppet who instead of being featured onstage is confined to the closet. Closet muppets are similar to other, more popular muppets, except that they lack the strong personalities, or they have slight cosmetic inconsistencies, such as the eyes are on crooked. The term generally is used to refer to people who are odd, unusual or have characteristics similar to a closet muppet.

Kermit: Are there any cute girls in your class?
Gonzo: Nah, they're all closet muppets.