Hulk Hogan, just rip your shirt a lot and you'll be good
[img]http://images2.wikia.nocookie.net/__cb20120311011755/serious/images/d/db/Beheaded_Kamikaze_sshd.png[/Go shirtless and hold two watermelons you spray painted black.The headless part would be tricky but decapitation can't be that hard.
Some duct tape and a piece of paper with "My costume this year is apathy." written on it.It's what I'm doing.