What are the unwritten rules about accepting or declining a rematch challenge?

I'm asking this question because I've just finished 3 games against the same opponent. He started out a with a bit higher ranking than me but did not play at that level. Our rankings are both about 950 and not that impressive, but he seriously played much worse than expected. After the first loss he challenged me. I though I'll give it a shot. Might be easy ranking points. The second game went along with the first. He blundered seriously and was put in mate pretty fast. I accepted yet another challenge and the story repeated. When the third challenge came I decided it was enough and declined. The opponent left me a note that endorsed me to grow some sportsman ship and in addition do things with myself that might be considered inappropriate by some people.

In other words: he was pissed.

So my question is: Was my acting wrong here? I'm new to this community.

To the OP. Your opponent is a moron. Block the blockhead.

I like an answer kaynight himself gave once in a similar situation: "I'm not forced to beat you twice, sir". Thrice in OP's case.

If we put it in writing, it's not unwritten. Nice try

Next time just keep beating him till he gets bored.

That could waste all day!

It is the internet.  The unwritten rule is that I leave whenever I have to, or whenever I feel like it, and I say something about it if I have time and if I feel like it.  If you don't accept that, then go find a chess club or make some real life friends.