Back at the old site I RP'd in, it was generally accepted that simple actions were okay. That is, you could make another character catch a ball that you threw, say hello back to you, etc. That was, however, an unofficial practice. The official practice was that you couldn't RP another character in any way. However, you could end your post with " *baton pass* ", indicating that it was alright for other RP'ers to control your character.