In a Saturday Night Live skit where Blue Öyster Cult is recording "(Don't Fear) The Reaper," Christopher Walken demands more cowbell from Will Ferrell, who complies. A catch phrase is born.
It's a Behind The Music sendup, with Walken playing producer Bruce Dickinson, sent to deliver a hit. When they run through the song, Ferrell plays the cowbell with alarming enthusiasm, but Walken loves it, ordering "more cowbell" and telling him to "really explore the studio space," which he does. Jimmy Fallon, playing the drummer, almost ruins the big by laughing his way through it. There really is a Bruce Dickinson, but he wasn't the band's producer - he worked on re-mastering the album, which is likely how his name got used. "More cowbell" becomes a popular catch phrase, handy in situations where a suggestion is warranted, especially with music. So when your friend plays you his demo, you can simply reply "needs more cowbell" instead of telling him what you really think. For BÖC frontman Eric Bloom, it's kind of annoying. In 2016, he tells Songfacts, "Somebody brings it up to me on a regular basis."