The Las Vegas waterfall is a sexual act in which a man urinates into a birthday hat. Then another person takes the urine and poors it down the man's back, while holding another birthday hat on his lower back in preperation to catch the remaining pee. As a result of this sexaul act, the man will climax. This act is called the "Las Vegas Waterfall" because prostitutes in Las Vegas have done this to an intoxicated man on his birthday.
by joeblow234 November 2, 2010