A Retarded Cousin is that one slice of pizza that is cut smaller than the rest, and is usually left-over, until drastic measures are used.
If left at a party, the host will usually try to trick someone into taking the Retarded Cousin home.

The phenomenon of having to come out as bisexual to the same person/people repeatedly because they assumed or hoped that your sexuality was a "phase." Refers less to the holiday and more to the 1993 Bill Murray comedy film in which the main character experiences the same day over and over.