"you're a towel is a meme that began episode 144 of the hit comedy central show South Park. During the episode the main focus of the episode Towelie is having an argument over a novel he wrote and he is arguing the he is indeed a human when someone would call him a towel he would simply replay with "you're a towel" After which it began to be used in many viral videos, when someone was losing an arguement they would just say "you're a towel" and the Idea was that every comment after that made by the aformentioned "winner" was absolutely invalid. Linking it with the other famous meme "Your arguement it invalid."