Today You Learned - a spinoff of the term TIL, or Today I Learned. Used when responding to someone who realizes something new that they've learned.
OP - "Me and my girlfriendlove edging. I drive here crazy in bed because she never knows when I'm going to take her all the way, or edge her and prolong our session."
Commenter - "Oh wow, I just realized my boyfriend's been doing this all along! Didn't know this was actually a thing."
1. Short for 'Text You Later'.
2. Short for 'Ten Years Later'. Used in anime/manga, often to make a character old enough to be depicted in sexual activities that are inappropriate or illegal for their age as given in the manga/anime.