All I can say is that honestly, I wish I had ever felt strongly enough in a show to boo. I recently saw a show at Lincoln Center Festival that ranked among the worse productions I've seen in my life, and really all it provoked in myself and the students I had taken with me was sleep.
I'm reaching my mind back and trying to remember some time being actually angry or upset at a poor performance.
Oh yeah, Karen Finley. I wish I'd booed her.
New standard: I think booing is rude when someone is simply doing a bad job. However, if you're confronted with an artist who is being deliberately hostile, insulting, or rude towards the audience, boo away! Remind them who is in charge.