The main thing is to not be so blatant about it.

Don't sing 'Sanctuary Watch' to the tune of Karma Police.

So does this mean my character can no longer sing songs that are kind of a knock-off of tenacious D? like no one can destroy the dragon, etc. etc.?

.... Not that he did.

The D's music is a beautiful, sacred thing that is not to be spoofed lightly, sir.

okay. no more spoofed D songs. got it. sorry bout that.

... not that I did. :P