Michelle Obama & Cleveland Cavaliers Do Mannequin Challenge In White House

(TMZ) -- Despite having a pretty rough week, Michelle Obama found some time to smile and goof around with LeBron and the rest of the Cavs on Thursday ... pulling off a Mannequin Challenge at the White House! 

The Cavs were at 1600 Penn. to be honored by Obama for winning the NBA championship -- and decided to get in on the social media craze while there. 

No sign of Barack ... guessing he wasn't in the mood. 

Photo: Getty Images