I don't find it odd, in the sense that everyone seems to call him that.
Personally, I don't like it. I would imagine Johnson does quite like it. It's cheerful, and upbeat, even when it maybe isn't meant to sound that way.
It's the soubriquet of the clown: remember Angle Eagle's reaction when he was appointed Foreign Secretary? She burst out laughing.
It implies that his friends love him and his enemies fundamentally don't take him seriously. I dare say he's happy with that. It feels like a bit of a let-off to me.