Happy face, Mean Face

Grayson will randomly say, "Mommy, happy face.", and we both smile at each other and then he'll say, "Mommy, mean face." and we'll both give our best scowl. This can happen at any point; while I'm cooking, while we're in the car, while I'm paying for groceries, doesn't matter. Everything stops to do "happy face, mean face." Guess it's just one of our 'things' right now.