Finish the sentence, ideally with examples that have actually happened to you. Saw one of these threads on another forum, and some of the results were pretty fantastic. 

[b]You know you have an RP Problem when...[/b]

Your original characters have conversations in your head. 

You've approached a real-life situation by thinking "What would [my character] do?"

You've stayed up to an ungodly hour waiting for someone to post. Or, alternatively, have set your alarm for the middle of the night in order to check for new posts.