Selective grammar

Tonight we were driving home, and Sass and Spyder had one of their typical "what if" conversations. I can't remember the exact topic, but it was something along the lines of "what if birds said 'woof' and cats said 'cheep cheep' and ducks said 'cockadoodle doo'?"

They play these sorts of games often, and I was only half-listening until I heard Spyder say, "That ain't right!"

As usual, I immediately popped in with, "No, honey, you should say 'that isn't right'."

Spyder's unexpected reply was, "No, Mom. I'm using bad grammar to make my point!"