When you stalk your RP partner and see him/her looking over the RP thread
Waiting for such RP partner to post
Realizing that RP partner logs off
When you have an OC you want to ship with someone else's OC and the partner starts to think the same
When those two OCs hook up and become canon
When you kill off your own character
When you have a favorite OC that's all cute and innocent and sweet
When you have a favorite OC that's a villain