Seven of Nine in Star Trek Voyager. She is blunt and tactless, and has little idea of how to socialise. Although it could be argued this is broguth about by her upbringing, the character could have been based on someone in realf life with a similar outlook, brought about by aspergers.
Harvey Pekar in American Splendor (the film), as well as his colleague.
Anya in Buffy the Vampire Slayer (the later series, anyway) resembles one, in that she is sometimes naieve, and in one scene where a person has died she complains that nobody will tell her how she's supposed to act. Also in an episode about her past she mentions people have objected to her 'taking things literally'.