Characters
(singing) "The hero of Canton, the man they call 'me'."
— Jayne ‧ Firefly

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker sings a grand, self-congratulating tune about being the hero of a place, and the punchline is that the hero's name is just 'me'. The humour is in the brazen self-praise, dressed up as a proper ballad.
Context reviewed