Give the extra polite behavior that really means 'fuck you'. For ex. "Have a *nice* day." (complete with big insincere smile)

And what can anyone say? Shame on you for being nice to your sister?

My only other advice involves a stick and a human pinata. Which might get you arrested. So, you didn't read that.

Other than that, not much you can do when it comes to family. Avoidance, maybe? I have family members I haven't spoken to in years.