Flagging your opponent!

So is it bad sportsmanship to flag your opponent that is in time trouble?

Let me give you an example. 
You know that you are -14 in material and but you have 2 minutes left. Your opponent is struggling to find checkmate and has only 12 seconds left on the clock. 

Is it bad sportsmanship to make stalling moves to win the game on time?

What are your opinions on this?

If you are wondering what "flagging" is https://www.chess.com/terms/flagging-chess

I think it's fine. If they allowed themselves to get their time so low, it's partly their fault.

Yeah, its fine

They took their time for thinking bout good moves and got into time trouble

Play with increment. That puts the focus back on chess instead of on the clock.

I think it depends, if your interest is just having fun and hanging out, then it shouldn't matter if the habit is flagging your opponent. It is not interesting to prioritize a better quality game, what is important is to have fun and if your way of having fun is to win by time, that is not a crime.

For the player who intends to play the best he can or even wants to improve as a chess player, it is already different. If the resource to win is almost always flagging the opponent, then the player should be questioning himself with his game.
Already in a certain very high elo I think that in general that does not matter, already in itself it is a merit flagging your opponent when he is a very high level player (let's say 2600 blitz on chess dot com).

In bullet chess this does not matter at all.

I don't see why that would be bad sportsmanship. What other option do you have? Lose intentionally? Now that would be bad sportsmanship, no doubt.

No, it's not bad sportsmanship. Time control is part of that game since it was agreed to at the start. No different than a basketball team up by 1 with 15 seconds left, holding possession of the ball and running the clock out without attempting to score. An added time increment will always allow time for a move...not a good one maybe, but the opportunity to move. So play with an added increment if you want to avoid games with an intentional timeout (flagging) strategy.

Trash talking on chat is poor sportsmanship (unless agreed to beforehand). It would not be tolerated OTB in a rated game at a competition. Another type of that is emoji icon trash. You get a notification that your opponent wants to chat, you accept to see what it is. Then no communication other than a continuing cartoon string of emojis.....examples, applause hands for their move, a bomb with a lit fuse after their move, any number of mocking emoji faces. You just have to ignore it, since you cannot turn their emoji cartoon string off once you accept the chat request, they can send them for the rest of the game. Turn chat off and/or don't answer a chat request until game over.