Telling someone "this isn't interesting to you" in place of "I don't want to talk about it" is definitely not polite!
I'd say it's rude in general to tell someone they won't find something interesting, and especially so when it's done as a way of disowning your own preference not to talk about it.
I'd say it's rude in general to tell someone they won't find something interesting, and especially so when it's done as a way of disowning your own preference not to talk about it.