I do the exact same thing! Definitively a BPD characteristic. Sometimes I tell a lie, or "twist the truth" in a way that I end up believing it myself. I think it has a little to do with the fact that borderlines can be very manipulative people. I must admit that it's gotten me out of a lot of situations where the truth could have bring me a great deal of trouble. I'm not proud of it, but it comes so natural to me now that it's hard for me to stop.