As children we had a white bunny we gleefully decorated one year with some non-toxic edible vegetable dyes. The bunny was not amused. My poor mom could barely keep a straight face as she attempted to scold us.
In Speedway, Indiana (the little enclave where the Indianapolis 500 happens,) one family dyes its poodle in a black-and-white checkered-flag pattern every May.
Since that one excellent (but carcinogenic) red dye was banned, cooks have nearly abandoned the Red Velvet Cake. The new dye is more likely to surprise the cook (or the dog-dyer) with a brownish red than the old one.
Beets have a rather persistant pigment. After one season of growing beets in the garden, my wife said she would no longer cook fresh beets. Your redness may vary, especially if your friend has white furniture or carpets. 
Another vote for funny! Especially if your friend is a guy, the pranks my roomates and I participated in were always met with warm appreciation. Even that one time we turned Tim’s room into the largest E-Z bake oven ever constructed.
Whatever you do, don’t piss off the rabbit.
