Brooke Mueller -- Getting DOWN Before Drug Arrest [VIDEO]

Minutes after Brooke Mueller allegedly assaulted someone Friday night, she sashayed her ass into an Aspen nightclub like nothing just happened -- and TMZ has the hilarious security cam footage.

TMZ broke the story ... Brooke was arrested Friday night outside Aspen's Escobar nightclub on suspicion of felony cocaine possession. She was also booked for third degree assault after allegedly attacking someone at a different nightclub nearby.

But right before all that happened, Brooke DANCED HER FACE OFF.

There's no sound -- but you can totally make out Brooke doing her thing ... twirling around, drink in hand, bumping into other dancers. Moments later, cops show up and drag her outside.