face diarea
When your face gives you away and shows you're thinking 'why would anyone say that' or 'this is the stupidest thing I've ever heard' while you're trying to act like you're listening.
He looked like he had been told he had to eat a whole cake for breakfast.
She looked like she had just been insulted by a dog.
His face was like he had just been asked to solve a math problem by a chicken.