Someone needs to remind Roseanne Barr her ass is 61 years old ... 'cause last night she was shaking it like it belonged to Miley Cyrus.
The new slimmed down Roseanne jumped on stage at the Comedy Store on Sunset with comedian Red Grant -- and when the DJ dropped "30 Deep" by Chevy Woods ... RB got real loose.
By the way, some of the lyrics she's freaking to:
Jokers to the left and the rightSee all my n*****Same n***** that I started withAll my n*****
At least she didn't sing along.