I only do that if they're being obnoxious and not resigning.
Do you like to torture your opponent?

I personally feel that dishonors your opponent, especially if it's an important/tournament match.
Also, there's a counter: they can just leave the room and let their time run down till they lose.

Say mate in 2. I am a feeble 1200 and playing 1900. I wait for 14 days to run dry then all of sudden - the moment he least expects it BAM!!! The obvious move.
Of course it doesn't work, as it triggers a conditional move to mate me. But it takes away the fun from him to mate me. I basically dictated the trigger.
It's a bit like premature ej....

I have found a fun way to really upset my opponent. All you have to do is play your game until you reach the point where you can mate your opponent in one move. Then sit on your hands while your clock slowly ticks down. When the time on your clock reaches its last second, then you make your move and mate him!
poor sportsmanship at its finest. and a waste of time

It's a fair thing to do:
- there is no rule on this site against not resigning when clearly lost, so your opponent can and often will waste your time out of spite
- but there is also no rule against taking your time to find the best move, so you can at least waste some of his time right back at him
...unless he realizes he can resign to avoid this, of course.
I have found a fun way to really upset my opponent. All you have to do is play your game until you reach the point where you can mate your opponent in one move. Then sit on your hands while your clock slowly ticks down. When the time on your clock reaches its last second, then you make your move and mate him!