Michelle Rodriguez & Cara Delevingne -- Grind Out a Threesome with Beyonce's Dancer

Michelle Rodriguez and Cara Delevingne spiced things up last night ... making a hot man sandwich by twerking and grinding all over a dude in London.

M-Rod and Cara hit up Chinawhite nightclub after Beyonce's concert, and took over the dance floor with two of Bey's male dancers -- but the highlight was a menage a trois.

Because sometimes life is awesome ... the ladies ended up straddling one of the guys, and let's just say ... his legs are now very familiar with their crotches.