Also known as the penis. There is no muscle in the penis, the penis is erect by a massive rush of blood. Therefore another nickname for the penis is the Main Vain.
by Butcher Jadali August 27, 2009
by justout October 02, 2006
by Nttm May 12, 2010
by gareth matthews January 28, 2007
did you hear about Leslie!? last weekend she was railing the main vain on a cruise ship and now shes married to a 65 year old millionaire.
by Jerry Himself August 02, 2017