Left 4 Dead

another achievment best completed in a local Versus match with two controllers. set your main gamertag to a survivor and the guest to the infected.

go to no mercy episode 4 in the the hospital. from here just open the door from the saferoom so you can spawn your guest account. he will always come up as a smoker first, so kill him and then wait for it to respawn as a boomer.

position your boomer around a corner in the hallway so that you are the first one to encounter and kill him, before the AI survivors get the chance.

have your main character walk around the corner and quickly give the boomer a punch using the left trigger. take a few steps back quickly and then open fire using an auto shotgun.

Very simple achievement.

Note: To make this a bit easier turn FULL CAPTIONS on. To do so go into Options -> Audio/Video -> Captions -> Full Captions

Be on the lookout for boomers and when you see one melee him as SOON as you can.

Back up far enough so his explosion wont hit you, or any other player for that matter.

Shoot him and kill him before he stops stumbling (I'm not sure if the achievement will count if you kill him after he finishes stumbling, but I got this on 3 accounts ALL before he stopped stumbling)

If you don't back up far enough and get exploded on then you wont get the achievement. But don't worry as there are several boomers in any given level, more boomers for the longer it takes you.

When you try for the achievement make sure none of the other players are close to the boomer as NO-ONE can come into contact with the bile.

Play versus with a friend make sure there a boomer. Then the suvivor kill the other survivers. Then go up to the boomer an melle them then step back an shoot.make sure you don't get puked on

I got this achievement on accident while going for Zombie Genocidest. (All credit for the solution I was using for that goes to Turonel.) So, if you're going for that achievement, you might as well go for this one too if you don't already have it. Besides, if I can do it on accident, then it should be no problem for someone wanting to do it on purpose.

Best part is you don't need a second controller or a partner for this.

First, the set up:

1. Start up the final chapter of the No Mercy campaign on Expert in solo mode.
2. Kill all of your AI companions. I recommend the shotgun for this.
3. Grab a pipe bomb.
4. Exit the safe room, and make sure to clear any zombies in the stairwell so that you can get back to the safe room quickly.
5. Enter the hallway at the top of the stairs, and let the pipe bomb down it. This will trigger several special infected to spawn, one of which will be a boomer.
6. Book it back to the safe room and close the door behind you. The infected will follow. Just melee anything that comes to the door. Just make sure to stand back a bit from the door to keep from getting injured.

Now, this might take a little bit of time, but eventually the boomer will wander down to where you can melee him. When he does, get close to the door and melee him, back up a little, and then plug a shotgun round into him. This will make him explode goo everywhere, but being behind the door you should be protected from the spatter.

If you do manage to get hit, no big loss, another boomer will spawn soon enough and you can try again. I did it this way on my first (accidental) try.