A colloquial term describing someone or something as top quality; Evolved from a statement used to describe the quality of a guitar (able to be stood upon), later adapted to describe the level of physical attractiveness of member belonging to the opposite sex.
"Look, he is standing on that guitar!"
Person 1: "Look at that cute blond by the front of the stage."
Person 2: "I'd stand on that."
Person 1: "What about that other girl?
Person 2: "Oh yeah, stand."
Person 1: "And her?"
Person 2: "Stand."