A series of jokes that are increasingly popular with angsty teens.
(One of the funnier dead baby jokes)
Emo: Whats worse than a pile of a thousand dead babies?
Normal Person: I'm probably gunna regret this but, what?
Emo: The one at the bottom eating its way out!
Normal Person: *while laughing* Ah! Thats just sick!!!
A referance to the episode of South Park where the Family Guy writing staff was trained manitees. In short, a manitee joke is a random (and often stupid) joke that has nothing to do with the plot/storyline of a show.