Irish Car Bomb is:
1/2 to 3/4 pint of Guiness
Take shot glass with 1/2 shot Bailey's Irish Cream and 1/2 shot Jameson Whiskey
Drop shot glass into the Guiness and pound it.
Mmmm Mmmm Good! Gotta do it fast though, or the Baileys curdles and then it's just bad.
But oh so tasty!

Edit: As seen here