Ruby Rose -- Oysters with Karrueche Tran ... But She's Really Into Justin Bieber's Scent (VIDEO)

Ruby Rose and Karrueche Tran hooked up -- for dinner -- but Ruby's still thinking about her weekend encounter with Justin Bieber ... where he passed her smell test with flying colors.

Ruby and Karrueche (hypothetical couple name: Rurrueche?) hit up E.P. & L.P. restaurant Monday night in L.A. -- no coincidence, we're thinking, since KT recently tweeted about her crush on the "Orange Is the New Black" star.

But on the way in, Ruby talked about her Bieber encounter in Vegas ... confessing, he smells great and has something she desperately wants for herself.

As for Rurrueche ... the ladies told us all about their aphrodisiac meal, and addressed the white elephant -- what Rose's fiancée of just a few months thinks about random men and women (no offense, Karrueche) lusting for her.