Mat shot is nasty. As a germaphobe I'm officially ready to puke.

As for the Irish Car Bomb, 1) don't call it that while in Ireland, just ask for a car bomb. 2) It should only be done with Guinness draft, either from a keg or keg can. And typically you fill the pint glass 2/3rds full. Drop the shot glass in, wait about 1-2 seconds, then chug quickly, if you don't wait 1-2 seconds, the flavors won't blend to create a tasty alcoholic version of chocolate milk, if you wait any longer though, the alcohols and sugars start to coagulate and that's just nasty. This is how they roll in Ireland, and it's a wonderful treat.