I don't think Breakfast at Tiffany's has a fandom, at least in the fic-producing sense. I can't off the top of my head think of any classic Hollywood movies with fandom, which is kind of sad. I could read so much White Christmas fic, for instance. Or Singin' in the Rain OT3. Oh, oh! Or His Girl Friday fic! Although the dialogue would be hell to write for that.