A good Straight friend of a gay individual that is still in the closet. Tends to help the gay friend stay in the closet.
Enrique Iglesias was Ricky Martin's Closet Friend, he always knew Ricky was gay after watching him sing Livin' La Vida Loca... But decided to help him keep the secret.
Enrique: Ricky you are so gay, livin la what?
Ricky: Livin La Vida Loca Closeta Amigo! (Closet Friend!)
a nerdy or embarassing friend that you hide from your other "cooler" friends.
I asked my closet friend Sue to help me with my report but didn't invite her to my party.