You might remember GWAR as the outrageously-costumed band of troglodytes favored by Beavis and Butt-Head... well, here's a video of Oderus Urungus and his pals "caroling" in suburbia, with predictably silly/gory results.

However, if you prefer your metal less "gore" and more "glam" (but still equally silly) here's Sniper, a parody/homage band featuring comedians Chris Hardwick, Rob Huebel, and others. This video for "All I Want for Christmas (Is to Rock)" is a year old, but the song itself is easily as good as anything released in the '80s by Poison or Stryper.