See:
http://loudermilk.org/milk/
http://claytoncubitt.com/bets/grant/milk/
http://www.wral.com/news/3395948/detail.html
http://www.girlspoop.com/MOVIES/REAL...nChallenge.WMV
Usually there's the condition of not being allowed to vomit for a set amount of time after you're done with the milk. It is possible, but very rare to complete this challenge. You should be getting odds on the bet.