Michelle Obama -- WATCH ME DUNK THIS BASKETBALL ... In the White House!

Michelle Obama teamed up with LeBron James for one of the the most historic video bombs of all time -- throwing down a MONSTER JAM in the White House ... with a post-dunk STARE DOWN.

It all went down while the Heat were hanging out at the President's house last week -- working with the First Lady to promote her "Let's Move!" campaign.

While a couple of the guys were talking to the camera about the importance of exercise, LeBron snuck behind the gang with a mini-hoop ... and Flotus delivers a one-handed slam!

The best part ... the way she stares down the camera after the dunk. Classic.