pink unicorn (n):

A feature requested (eventually demanded) by a client that is not supported by the base system and lives in its own (name)space and time. Pink Unicorns must be fed on pure fairy dust and need a lot of maintenance - they are picky drama queens and often cause stress.

"What the hell is this parameter? It doesn't seem to be used anywhere! How did that happen?"

"Well, when a red unicorn and a white unicorn love each other very much..."