i would say, "hey aunt bella, wormtail called, he wants to know what time te want him to pick te up for cena 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 te have to do is just speak when you're not spoken to and wala! te have a pissed Bellatrix!