When I'm in a slump, I comfort myself by saying if I believe in dinosaurs, then somewhere, they must be believing in me. And if they believe in me, then I can believe in me. Then I bust out.
~Mookie Wilson, World Series champion
Don't get me wrong, there are messages of hope in a lot of Dylan songs, but they aren't exactly celebratory.
I briefly considered Forever Young but that seems too on the nose as a guy is turning 76.
Finally, it came to me: The Man in Me. In my opinion, this is the happiest Dylan song there is. For me personally, it helps that it was featured prominently in one of my favorite movies ever. But you're about to learn that if you watch the video.
Anyway, happy birthday, Bob! May we keep celebrating you for years to come.