Don’t make me laugh
Definition 1 of 1
Pro Tip 1/3Expressing Disbelief
Use this phrase when you think someone's statement is completely unbelievable or unrealistic. 
He said he'd never eaten a pizza before—don't make me laugh!
Pro Tip 2/3Showing Scorn
It can convey a strong sense of derision or contempt for what someone else has said. 
She claims she can speak ten languages fluently—don't make me laugh.
Pro Tip 3/3Colloquial Use
It's informal and mostly used in casual conversations, not in formal or serious situations. 
A unicorn as a pet? Don't make me laugh.