tlts;dr
Stands for "Too long to send, didn't read."

Meant to be for if someone sends you a message, you reply and then they don't reply for a few hours/days/weeks/months/years/decades and acts like it had been a minute. This shows your hate for what they have done and that you no longer care about the topic originally mentioned.
guy: Hey, what are you doing?
man: Nothing much, you?

2 days later

guy: Just playing some games.
man: tlts;dr