Is it okay to dirty flag in Blitz/Bullet?
Different situations call for different etiquette, but overall, flagging is part of the game and even if one situation is "poor etiquette", they can't blame you too much because you are trying to win. Besides, both players agreed to the time control; them not using time management as well as you is part of the game.
There's nothing "dirty" about flagging, because the player who loses on time does so because of his own actions.
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Players like to blame their opponents when they lose on time, but really - it's their own fault.
I do it in each and every game, and so should you! Flagging is the moto of blitz and bullet. How can you doubt the motto? If your opponent says "you won only because of time", then he's one of those players who like to blame others for their loss.
I am absolutely crushing my opponents when I lose on time. They're often just running with their king, sacking all their pieces and counting on the clock. It sucks when I dominate so thoroughly on the board while still moving quickly but are forced to think at least a little bit to mate them.
They ARE dirty flaggers.
"The Clock is a Piece"
In the early days they did not have clocks. Then there were complaints that a certain player was taking 1 hr per move and boring his opponents to death. So they invented the chess clock.
Two years later, I have won plenty of bullet games by dirty flagging. If you are playing without an increment, it is a legit part of the game. I have also been dirty flagged, and that's okay.