YOTL is from a DoraxBTS crack au created by filmfics on Twitter. It is an abbreviation meaning "You're on the list". You would typically use this when someone says something you disagree with.
Person 1: Have you seen that au yet?
Person 2: Yeah, it was kind of boring. I didn't like it very much.
Person 1: YOTL
Person 2: Yeah, it was kind of boring. I didn't like it very much.
Person 1: YOTL
by heckle keckle July 12, 2018