Rihanna is putting one of her pals to work, work, work, work, work ... having a woman come over and rub her famous backside down with whipped oil body cream from her own brand.
The singer-songwriter appeared in a quick clip posted to a pair of Fenty Instagram accounts ... lying on her front in bright pink lingerie -- when a feminine hand dips into a small cannister of Fenty Skin Butta Drop Whipped Oil Body Cream and goes to town on RiRi's booty.
Check out the vid ... Rihanna gets a pretty thorough rub on her exposed cheeks -- and, the video even slows down to give Fenty fans a good look at the jiggle.
In the caption, Rihanna pushes the Butta Drop and the Lavish Lace collection lingerie she's wearing ... a 2-for-1 sales pitch.
Rihanna's pushed her Fenty lingerie hard in recent weeks ... regularly stripping down to near-nothing to impress prospective buyers.
BTW ... fans are loving the marketing ploy in the comments, with some saying they'd give anything to be the person charged with rubbing Rihanna down.
A tub of the Butta Drop costs about $25, depending on where ya shop ... and, it'll get your butt shining bright like a diamond, just like Rihanna's.