I sorta half-listened to this interview while cleaning my bathroom the other day. While listening, I thought Harrison was being sorta rude to Conan, and really boring on top of that. I now realize that he just had some fantastic kush and was probably slightly paranoid.
Why would he not just be doing a character? The whole "Harrison for is high" thing started on a blog that got linked off reddit. My guess is this was done intentionally to go viral.