I've never felt offended when an opponent has played on to the bitter end. There's nothing about it in the rules, such as that it's even unsportsmanlike to do so. Personally I think the side that is losing is doing most of the suffering, though maybe it might not be the nicest thing if the losing side knew that the other player was, say, a child that had a parent worried about their not making it home for bedtime. Even so, it's not against the rules.
Btw, sometimes when people think they have the upper hand (or just have gained it), or even equalized from a bad position, they might smile, stare or (nowadays) crack their knuckles, it seems, though that might be just asking for an objection to the arbiter by the inferior side, if they felt offended or opportunistic enough.
IMO, changing the rules to the effect that an arbiter can arbitrarily decide when a position is clearly and easily lost (along with judging clock times and the relative strength of the players), and then declare the game to be over, would go against the relative purity and spirit of the game. That's not even taking into account the guesswork involved in assuming the superior side wouldn't make significant error(s) if the game were to continue instead.
Last edited by Kevin Pacey; 08-03-2018 at 01:27 PM.
Reason: Adding content
There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.
Hamlet (1.5.167-8), Hamlet to Horatio.