Can't really speak for RP vs non RP servers but I had no negativity levelling up until I hit outlands (on a PVE server) around 62ish. Now, during the day I can quest/instance do whatever all day long with no problems, but in the evenings I'm constantly being followed, whispered, etc - which I would assume is just the result of more people being online during that time thus increasing the overall chance someone is going to be a tool.