Because it was hilarious how controlling she was. It's like a racist joke: the humor comes from how rude it is. You recognize the rudeness/ignorance as humor since, for the most part, the person telling the joke is just trying to get a rise out of someone. I think it's no different with this: it's hilarious because she wants to be seen as an elegant, graceful, beautiful woman, but people mess with her and look at her in a way she doesn't want, so she does a complete 180 and resorts to karate chopping them