Writing "@dang" does not notify dang, though he sometimes stumbles across these questions. Email hn@ycombinator.com. I have always received a response to my emails in a day or less.

If I understand correctly, "flag" mostly doesn't come from dang. It comes from other users.

I think dang can flag a post himself, but more likely it's from users. It takes more than one user to mark it as flagged; I don't know how many it takes.