I was flying Air Portugal EWR-LIS, sitting next to a guy whose wife and child were in front of us. They were talking amongst themselves mostly in English and sometimes in German, while I spoke to the crew in Portuguese and chatted to a lady across the aisle in English.

As we started taxiing, the wife turns back to the husband:
She: Aren't you going to make conversation with your travel mate (me)?
He: Why?
She: Just to be nice and polite.
He: I don't have to talk to strangers. I'm not here to make friends.
She: Say, at least, "Have a nice flight".
He: No, I don't care.

They said all that in German, thinking it would be some kind of private conversation, but I do happen to speak German too.
If the conversation had gone ugly (about me), I would react, but it wasn't necessary.