Great post which is both easy and really hard to answer. I mean any number of photographers fit into the category of someone I'd like to have dinner with. I like eating dinner and I like talking about photography so it's a bit of a win/win really.
I already had dinner with some of my fave photo people: Skorj and Susan B on one occasion and Don Brice, El Gordo (sporting normal hair), Leon and Damion on another, but if you were to press me and I absolutely HAD to narrow it down to a single person I'd reluctantly cancel the seating arrangement featuring Simon Norfolk, William Eggleston, Robert Frank, Fazal Sheikh, Anders Petersen, Josef Koudelka, James Fee and some others and move to a small corner table in a bustling little cafe somewhere in the Big Bad City in the dead of night and get Weegee to tell me all about it. About everything. What a night that would be!!