The only official holiday for an animal behaving badly that I know of, Dead Duck Day has been celebrated on June 5 for the past 13 years at the Natural History Museum of Rotterdam. It commemorates the victim of the first scientifically documented case of homosexual necrophilia in the mallard duck, described in the abstract of the full original article thusly:
On 5 June 1995 an adult male mallard (Anas platyrhynchos) collided with the glass façade of the Natuurhistorisch Museum Rotterdam and died. Another drake mallard raped the corpse almost continuously for 75 minutes. Then the author disturbed the scene and secured the dead duck. Dissection showed that the rape-victim indeed was of the male sex.
The research was awarded the Ig Nobel Prize for Biology in 2003, and you can read about last year's celebration of Dead Duck Day at the Annals of Improbable Research, here and here.
Photo: a Drake mallard (Anas platyrhynchos) in full breeding plumage (left) next to the dead drake mallard (NMR 9997-00232) just after collision with the new wing of the Natuurhistorisch Museum Rotterdam; b the same couple during copulation, two minutes after photo a was taken. [photo: C.W. Moeliker]