Stands for "rolling on the bed squealing." Basically means the same thing as ROMBS, which stands for "rolling on my bed squealing."
This phenomenon usually occurs among girls when they discover or encounter something irresistibly, ridiculously, and/or irrevocably adorable.
Friend 1: So my friend proposed to the girl that he'd been dating on for 5 years by setting up a Gatsby-esque party and getting down on one knee at the lat slow dance with a bouquet of her favorite flowers!
Friend 2: OMG, ROTBS!!!!!!!!!