When I was in law school, I dated a girl who could lie right straight to your face and show absolutely no sign that she was telling a lie or felt bad about doing so.
She did a lot of bizarre things (including constantly telling me that she knew people who could have me killed and saying that I left the cabinet door open again she would take a knife and stab me). But lying so well was the only one that really scared the living hell out of me. "OK, [name of girl] let's go to the grocery store...." What? "Well, you said 5 minutes ago that you wanted to go." No, I did not. "Well, wait, you did." No.
Then I would stare at her and she would wait 20 seconds and say, "see how well I lie." Jesus. Yeah, real funny. I forgot I had Torts homework tonight....see ya!