I'm under the impression that Nic Cage doesn't know he's an actor, and thinks that all the stuff we saw on screen really happened to him.
Honestly, I bet Tom Cruise would go for that hook line and sinker. Also Gwenyth Paltrow.
Sometimes I watch Its Always Sunny and think, "Danny Devito doesn't even know he's on a show."
Daniel Day Lewis. Exploit his extreme method acting approach in some way and secretly video the results.