I would kill someone for this!

[Insanecowposse]

http://punchbaby.com/2010/03/nasty-tampon-prank-ftw/

if for whatever reason you can't use the link this girl concocted a fake bloody tampon and slapped a dude in the mouth with it and he proceeded to throw up until he started puking blood. She also convinced him it was real and not fake even after the vomiting commenced.
ps It looks like a fake reaction and the guy forced himself to puke.