Keep a list of such opponents and then do not play them again is my suggestion.
Frustrating!

it may be the case that he was thinking every move in chance for a stalemate...but i doubt it....it happens when your opponent tries to annoy you and make you resign of boredom,he could actually try to get stalemated but it's highly impossible since he spent 15 mins and when you try to get a draw out of nowhere you do not try to lose on time....

I usually just go get myself a cup of coffee and catch up on the news if someone pulls this on me. I just make sure I come back with a few minutes to spare.
And of course, put them on a do-not-play list.

I like to go check out the forums and block them, but it's still annoying.
There would have been no stalemate! I can do the K+Q v K mate in my sleep. I was actually thinking of promoting to a rook and practicing that, but that's still something I can do in my sleep. If it's a knight + bishop, I'm offering a draw...

this kind of thing happens in OTB a lot as well, especially at the scholastic level. I know at least one prominent chess.com member who did this a while back, he couldn't stop his opponent from promoting, so he sat there for 30+ minutes.
It was your British clone, Shadowknight999, right? Maybe Shadowknight00189998819991197253.
After offering 5 draw offers, my opponent took 15 minutes to find their next move and lost on time. Why does it take 15 minutes to find the next move when there are just 2 squares, meaning it took at least 7.5 minutes to think about each square.
Seriously, this crap is annoying. Instead resigning or a quick checkmate, they'd rather waste their time and violate the fair play policy. A rematch also would have been fun.
Yes, I know people post about this stuff every day.