The Annie Hall Wikipedia page says that the actual Truman Capote appears (starting around the :22 mark) when Woody Allen says to Diane Keaton “there’s the winner of the Truman Capote lookalike contest.” Wrong. The impostor doesn’t have that fearless Capote stride, and his hair is certainly too dark and too long.

Until this morning I’d never read or realized that Sigourney Weaver has a wordless, too-far-away-to-be-recognized cameo near the very end (:16 mark), standing under the Thalia marquee with Allen, Keaton and some guy playing Keaton’s date: