I think I know I WBU. In fact, I have brought shame on MN by stooping to these levels rather than just smirking and ignoring. I apologise.
I arrived early with DS2 to library rhymetime and was sitting reading quietly in the corner. Other mum comes in and announces to the whole place to her toddler that they will now sit and read. Cue LOUD reading of and over the top expressions and actions to the disinterested child. Very LOUD and ARTICULATED. And for some reason, I decided to out-loud-parent her and do the same, but going up one, by reading the bilingual books 
In my defence, I did very quickly get a grip and stop.
She didn't, though. Went on for another 15 minutes and then was the loudest singer with the biggest actions during Rhymetime. Her dc did I mention his name was Zebediah? was more interested in making piles of books and picking his nose.