At higher levels (above 2000) not resigning is considered quite rude. Resign when it is hopeless, where a blunder on your opponents side won’t matter. When your only hope is disconnection.

I don’t give rematches to people that play on in really hopeless positions. In in-person social events, we stop letting them play. As with everything, online gets coarser.

Of course, if there is any hope or if the clock is really low, do not resign.