I defy you/anyone to do something
Definition 1 of 1
Pro Tip 1/3Emotional Intensity
Expresses strong belief that the task is nearly impossible or evokes strong emotion. 
I defy you to find a happier couple than those two.
Pro Tip 2/3Implicit Provocation
When used, it provokes someone indirectly, urging them to prove the speaker wrong. 
I defy anyone to say this wasn't the best game of the season.
Pro Tip 3/3Not Always Literal
Often used hyperbolically to emphasize a point rather than to issue an actual challenge. 
I defy you to watch that scene without laughing.