Uwe Boll, two months ago. I would summon a time portal to appear about ten feet in front of him when he was alone (or better yet, during filming), and say, in a majestic voice "Are you filmmaker Uwe Boll?". He would answer, scared or curious, to the affirmative. I would then say "You're a massive douche. I just thought you should know that before you die." While he's confused, I would quickly punch him in the face and retreat to the present before he knows what the fuck.