The phrase comes from a Saturday Night Live sketch first aired in 2000, in which Christopher Walken plays record producer Bruce Dickinson during a fictional recording session for Blue Oyster Cult's Don't Fear The Reaper. Will Ferrell's cowbell player, Gene Frenkle, keeps playing louder as Walken insists the song needs more cowbell. The sketch became one of the show's most quoted moments, spreading through reruns, video clips and internet memes, and it endures because the deadpan demand works as shorthand for pushing anything further than it reasonably should go.