For anyone else who wants to see, put the .dem file in C:/program files/steam/steamapps/<yourusername>/team fortress 2/tf/
Then open up TF2, type demoui in console (to pause), then type playdemo rudedogsings.
Oh, you'll need this map to play the demo:
viewtopic.php?f=38&t=21704
The sound won't sync up with the singing at the start of the demo, since the music starts at the start of the demo but it is really supposed to start at the start of the map (recording a demo halfway through a map with music is bound to mess things up, my bad) but after that first round ends, the music stops and starts up again, and you can marvel in rudedog's vocal prowess
Um... It won't let me upload to the forum (it blanks out the message and doesn't show that it's attached), so I uploaded it to this:
http://www.mediafire.com/file/g24cnnyum ... gsings.dem