Phrase used to describe someone who is very gay by someone who is either homophobic or an asshat. Eric Cartman used it to describe Stan's dog Sparky in one of the first episodes of 'South Park' in 1995.
Credited to Trey Parker and Matt Stone.
"Stan, your dog is a gay homosexual!" Eric Cartman, upon witnessing Stan's dog Sparky hump another dog at the beginning of the episode titled 'Big Gay Al's Big Gay Boat Ride'.