facial erection
The face someone makes when they see you and it’s like their brain short-circuited. They’re too turned on to think straight, and it’s both hilarious and terrifying.
He saw me and his face looked like a dog who just got a treat and a pat on the head.
She walked in and his face went from normal to ‘I need a drink’ in 0.5 seconds.
He saw me in a hat and his face looked like he’d just been told he won the lottery and a free pizza.