i would say, "hey aunt bella, wormtail called, he wants to know what time you want him to pick you up for hapunan tonight." then her response would be"i never agreed to go out with wormtail, eww." then i would reply"i know, i agreed for you." then i would run for it before she torments my butt off.
I think that Bellatrix doesn't need a lot to have happen before she gets pissed off. I mean really, you've seen what has happened in the movies. Seems to me, all you have to do is just speak when you're not spoken to and wala! you have a pissed Bellatrix!