Left 4 Dead 2 Achievements

Location: Dark Carnival
Chapter 4: Barns

Look at the left once you past the bumper cars and you will see a whacking game called "Stache Whacker". Just like the achievement name. Anyways, just start the game once you see it and play!

Weapons might help with:
-Assault Rifle
-Desert Rifle
-AK-47
-Pistol (2)
-Melee weapon

Now, just press the button and shoot the egg that pops up. Just keep shooting or hitting alot. If it keeps saying continue, then keep doing it. The objective of this achievement is to keep shooting/hitting them. And once you hit 42 -45 times, then the game explodes! Once it explodes you have got the achievement!

So that's how you get the "Stache Whacker" achievement.