When you're in a chess match, and you're running low on time so the opponent decides to insta-move or premove his pieces to time you out and win. Be faster and don't get flagged!!!
Anish Giri: has 5 seconds on the clock Hikaru Nakamura: premoves the rest of the match
Anish: Not cool, Hikaru just flagged me!
Hikaru: There chat, I flagged him for content
A person who's a very obnoxious asshole. An anal flagger is someone who has passed the level of douchebag in their behavior and is headed for asshat status.
Steve: "Everyone hates Todd because he's so rude and obnoxious! He acts like such a douchebag!"
Ryan: "Yeah, Todd's a real anal flagger!"