I think RPer's are people that those who couldn't make the schools drama/theater (because you have USA in your location you are not british, please use the correct spelling for your location.) club or plays. So they go and subject people to their bad "acting" through text. They choose to "act" in text and from a character in a game because they can't act in real life.
I would say RPer's in the realm of acting are lower than clowns/mimes.