When you do or say something that makes you seem retarded. From the Hallmark Hall of Fame movie of the same name starring Rosie O'Donnell in which she plays a "challenged" person who, surprisingly, rides the bus with her sister. What could have been a touching portrayal was ruined by the fact that she spent the majority of the movie screaming and acting like an insane monkey rather than a noble portrayal of a person with mental handicaps. So really, you are acting more like an insane monkey than a retarded person. Can be shortened to Riding the Bus.
"Do you really think you should wear leggings under your skirt? It's a little Riding the Bus with My Sister."
"Don't talk so loud in the movie theater. It makes you too Riding the Bus With My Sister."