Take it seriously and do whatever I can to stop them. Maybe I'll become a Superhero and get my own anime/manga with thousands of fans and get rich. Maybe get a girl too.
Being an evil genius myself...I know how hard it is to think of a nice decent plan for world domination. I've seen it all, using rock music to destroy the world, burning bibles so God would get pissed, and something to do with a cat and a box. So I would give this person my bacon out of the evil in my heart...but I would charge him for it.