Since I have conscious dreams and barely had only one nightmare when I was a kid (Ripper Roo was in it, and now we're BFFs), I think I'd just try to act as calmly as possible and probaly:
1. Say how much I admired his work;
2. Polietely compliment the amazingness of his evil laugh;
3. Ask for an authograph;
4. Explain him what an authograph is if he doesn't know, thus setting up a much nicer mood;
5. And gaze at his greatness in silence. The rest is up to him.