Mom, you're vacillating!

Claire's teacher is a vocabulary buff and enjoys sharing new words with her class. Actually, I think she just likes to keep parents on their toes. 
Here's an example:  Last week the kids and I were at the store and I was trying to decide between two brands of juice- you know, reading the labels and checking for hfcs (high fructose corn syrup) so that my kids won't bounce off the walls any more than normal, and Claire says:
"Mom, you're vacillating!" 
"Wait, I'm what?" 
"Vacillating, mom- it means you are going back and forth between two things and can't make up your mind." 
"Oh, thanks Claire." 
Wait, that's my six year old? 
I had noticed that she'd been dropping some bigger words lately, but this was the first one I didn't know. Talk about humbling. So I thanked her for enriching my vocabulary (and got to teach her what enrich meant- take that, teacher!) and we moved on.

And another example: Yesterday she told her brother he was being truculent, and if he didn't stop she was going to ostracize him.  Do you think the teacher's gone too far? What next?