If just dinner:
That popular "Kony" guy
Hitler
and Darth Vader.
They'd either all get along amazingly well, or horribly. Either way it'd be hilarious. XD
(I'd have chosen Osama instead of Kony, but he's dead.

)
If somehow they keep existing in our reality after dinner:
My best friend
Leonardo Da Vinci
Either Fluttershy, Pinkie, or Gilda from MLP: FiM
Me and my friend are both huge bronies. And it'd be amazing to see what Leonardo would come up with in our age, given everything he did in the Renassance.