la-la-ing
letting someone think they're winning, then hitting them with the truth like they just failed a math test
You said you'd let her win the lottery. Then you told her she only won a scratch-off with a $10 prize. She thought it was a real lottery.
He told her she'd get a new car. Then he said it was a used minivan that smelled like a raccoon’s closet.
She thought she was getting a free trip to Paris. Then she found out it was a 2-hour bus ride to a hotel with a broken AC.
xs