Kanye West -- I'm Not Signing that Pic ... That's Kim's OTHER Wedding!

Kanye West had a sweet moment when he arrived in D.C. Sunday ... a fan wanted him to sign a pic of his bride on their wedding day ... problem is, the guy had the wrong groom!

Kanye and Kim were making their way to their limo when the autograph hound extended his arm, photo in hand. Turns out it was from wedding #2, when Kim married Kris Humphries.

You would think Kanye would have blanched, but this is the new, improved, hyper-social Kanye West!

Check it out ... it's hilarious.