The line comes from South Park, the animated series created by Trey Parker and Matt Stone that first aired in 1997. In the early seasons, Kenny McCormick was killed in almost every episode, prompting Stan Marsh to exclaim that they killed Kenny and Kyle Broflovski to call out the culprits. The gag became one of the show's most quoted running jokes and spread through clips, memes and reaction videos long after the deaths became less frequent. It endures because the phrase is instantly understood even by viewers who have never watched a full episode.