Creative Kareoke?

Have any of you ever gone to a kareoke bar and performed interesting filked versions of the songs, rather than the official lyrics? I'm not talking changing pronouns or names to sing to your sweetie; I'm talking full rewrites, all the verses, that rhyme and scan, on entirely different topics than the originals.

If not, does anyone else think doing this with a group, for a whole series of songs, would be a hell of a lot of fun?

Or am I just an incredible geek?