HAHA "unethical" Maybe your opponent did not know what unethical meant. I think he meant unsportsmanlike, unethical means that it is morally wrong. And no it is not unsportsmanlike to not offer a rematch, and it is definitely not unethical. Your opponent was obviously an idiot.
Is it unethical to not offer a rematch after winning a game?

Usually after they loss, they will ask you for rematches, one after the other, until they win one game. After that, they will dissapear in less than a second.

@Rybkat I didn't think it was, but perhaps there's a larger population who thinks it's unethical... or unsportsmanlike.
Speaking of "idiot," he had choice words to describe chess players who didn't offer rematches. I don't see why people choose to leave such antagonistic notes, messages, and posts on chess.com.
@SocialPanda It would be interesting to observe how often players ask and leave after losing. I've found most players are not interested in rematches.

@rooperi I agree the level of entitlement in such a belief is astounding. I also think the assumption that it's ethical when so far everyone seems to balk at the idea may indicate the player was out of touch...
or as @please_let_me_win concurs, had a desire to get back at the player and leave.
@Rybkat lol, I didn't even know we could post pictures. edit: and that is indead a good picture.

who cares what people think, do whatever you want :)
if u want to rematch, rematch, if not then dont. do whatever you want

who cares what people think, do whatever you want :)
if u want to rematch, rematch, if not then dont. do whatever you want
That large of a font is not necessary.

@Kasporov_Jr I care what people think, lol. I do want to ask, and I respect everyone's opinion.
I even respect the opinion of the player who thinks rematches mandatory, in so far as giving him enough credit to look it up.
Given everyone's responses so far, I do agree with your conclusion despite its basis in a different premise.
edit: fixed a typo

who cares what people think, do whatever you want :)
if u want to rematch, rematch, if not then dont. do whatever you want
But... but... what if I want people to behave like I want them to ?
Me, me, me, me and myself ! Whine !

Here is how I behave with rematches:
If I play a match and I totally crush my opponent and he asks me to play a rematch, I play so that we get to play with both colors. But if it is an "easy" victory again, I won't play more as it matters more to me to learn as much as possible than to get higher rating.
If I end up playing rather "drawish" game and it seems like we both are on the same level, I try to play as many matches as possible and focus a lot on winning the match. I don't hesitate to offer a rematch or accept one after the match even if I lose. Playing like 12 matches against the same opponent when each and every game is "balanced" feels awesome.
If I play vs a lot stronger opponent than myself, I sure do offer a rematch if I won't lose too badly as I hardly lose rating and I can any day get my old rating back. I also learn a lot so something like 0-5 score might be possible and I wouldn't mind.
BUT if the stronger opponent asks for a rematch, I decline as it feels like he just wants to get free ELO

Gosh, what a novel idea for a thread. I'm surprised this topic hasn't come up for discussion before.

Double or nothing? Losers have been asking this forever. Forget it, the beauty of online chess is never having to play to same person twice.

Gosh, what a novel idea for a thread. I'm surprised this topic hasn't come up for discussion before.
The thread is no less novel than your reponse.

@Estrinian Thank you for your input. I enjoy playing the same people again, but not necessarily on their terms and especially not in the face of insult or false claims of ettiquette.
@Ninzake Quite the elaborate approach given the simpler ones offered by others. Your emphasis on personal growth and focusing on more than rating is a nobile one.

who cares what people think, do whatever you want :)
if u want to rematch, rematch, if not then dont. do whatever you want
But... but... what if I want people to behave like I want them to ?
Me, me, me, me and myself ! Whine !
I sense that you don't condone a certain type of behavior....

Interestinly enough, one of my opponents declared the exact opposite when I offered him a rematch after winning a game. His own view was that it feels like you just want to pummel your opponent to the dust, as his mistakes will only worsen over time.
I personally am just happy to play. As long as you are a good sport I'll be happy to play another game!
I received a note from another player that said it is unethical not to offer a rematch after one has won a game.
Let's say a player offers a rematch and wins. Does ethics require him to offer another rematch and only stop until the opponent wins or declines a rematch?
If the opponent wins, does ethics require the opponent to offer a rematch?
What are your thoughts?