Left 4 Dead

As the achievement is still glitched online, here's an easy method to get it by yourself:

1. Set up a Versus System Link match with 2 controllers on the Crash Course campaign and the Truck Depot Finale chapter. Set your profile (controller 1) as the infected, and your Guest profile (controller 2) as the survivors.

2. Using your guest profile (controller 2), make your way to the end of the level you where you see the generator. Make sure that you pick up a pipe bomb on the way. There is sometimes a few just infront of where the ammo and first aid kits are at the end. Do not start the generator yet.

3. At this point restock ammo and health. Pick up a Fuel Can and place it at the bottom of the generator that you turn on to begin the finale.

4. Kill the 3 other AI survivors.

5. With your profile (controller 1) keep respawning as special infected by being killed by the remaining survivor until you are a Boomer.

6. Once you are a Boomer place yourself on top of the buses (by the ammo and first aid kits).

7. Turn on the generator with your Guest (controller 2) profile and then climb up the generator pole. Steps to climb it:
* Face the generator head on - bus to your back and ignition switch to your left.
* Walk up onto the hitch (no jump necessary).
* Hop up onto the first step.
* Hop up again onto the next step.
* Hop up a third time, and now you should be about eye level with the yellow wire on your left (it will look black if the lights are off).
* Hop up on more time by barely tapping a - this one might take a couple tries. When you've got it right your character will actually be crouching (check the view from the other controller's screen) and you'll be looking right at the back of the actual lights.

8. The horde will now attack but they shouldn't be able to reach you. However, occasionally one can climb up and hurt you so be careful. Shoot the Fuel Can below and watch them burn. Kill the remaining horde.

9. Once the horde has gone your main profile (controller 1) will become the tank and the AI will take control of the Boomer - Do not kill the Boomer!

10. Move the tank (controller 1) within shooting range of the survivor on the generator pole (controller 2) and then use whatever weapon you have to destroy the tank. The Boomer should now be right below you where the zombies were.

12. Your main profile (controller 1) should now spawn as a Hunter. As with the Tank move over to the survivor and then kill him.

13. You will now spawn as the Smoker (controller 1). Move the Smoker to the base of the generator.

14. Equip the Pipe Bomb and throw it so any zombies will leave you alone. Drop off from the generator pole and then either let the Boomer vomit on you or kill the Boomer so that he explodes on you.

15. Now use the Smoker to pull in the bile-covered Survivor and you should now have Slippery Pull. NOTE: Make sure there is nothing between the Smoker and the Survivor when pulling in otherwise the Survivor will get stuck on something and it will not unlock.

although these achievements can not be earned properly yet, system link is not the only way to achieve this. host a friends only game and invite other people who need the achievements on crash course, once your game is set up tap A repeatedly on the 'start the game' option. (try doing it as fast as you can as that tends to work with me) the game should instead of searching for a dedicated server, start the countdown straight away and host a local game where all the achievements are unlockable. the game will sometimes crash when trying to start this!!! but keep trying as it does work and makes it easier. ask me if you need any further help on this...

I hosted a vs game with a signed in guest account Make it so the guest is a human.
Than i selected play with frends --> changed the permissions to public and forced local host by smassing A (now the achievements is not glitched because you basicly play a local game)
Then waited until a random player joins the match (He will spawn as a boomer and you will be a smoker witch is what we want)
Than I walked the guest account a few steps out of the saferoom next to an corner
And than waited until the boomer (random player) puked over the guest account and smoked him direct after that
and the achievement popped up

Double Xbox Boosting Method Only - Only ONE Copy of the DLC and No Smashing "A" Needed

Please stop downvoting me if you only have one xbox - this solution is not for you, but it helps other people so I would like to keep it up.

EDIT: If you have this game in digital form you should only need one copy of the game (but two xboxes). Physical requires two.

This solution is only for people with two copies of the game and two accounts (I haven’t tried this on a silver account so try it out and let me know so I can update the solution. If you don’t have a second gold account then use a 48 hour trial which, if you are truly a gamer, you should have like 20 copies of that came free from all the games you own). This is the easiest method to get this achievement, hands down. Took me five minutes and you don’t need to download the DLC twice (just once!).

First, log into your main (home) xbox with the Crash Course DLC with the secondary account (the one not getting the achievement). See if it says that Crash Course is available. If not, then switch profiles to your primary account and it will boot you to the main menu. Hit start and the Crash Course DLC should show up. Now switch profiles back again to the secondary account and after going to the main menu hit start and the Crash Course DLC should now be available for the secondary account not tied to that xbox.

Put your primary account on the second xbox, load up L4D and then re-download the Crash Course DLC. Even though it’s not tied to that xbox, it’s tied to your profile so it will show up and now both accounts can use the DLC! (this works for most games so if your friend wants to come over and not buy the DLC he can get the achievements too – I’ve done it using my bro’s DLC for COD).

Sign in a second controller (guest) with the primary account. Create a system link game. I do not know why people keep screwing around with the stupid “smash the A button” routine and freezing their xbox. A system link game does not log into the dedicated servers so it allows you to get all the glitched achievements locally. You can even create a system link game on one xbox and not have to connect to anyone else.

Your primary account and the guest sign up as infected. The secondary account is human. When you first spawn, you will most likely be a smoker as the primary account and a boomer as the guest account – perfect! If not, then keep dying until you get the right combo of players.

Have the secondary account on the other xbox kill all the other AI players. Now just move that person out of the safe room. Have the primary and guest accounts spawn and just walk into position next to the human player. You can stand 10 feet away if you want since no one will kill you. Now just vomit on the secondary account with boomer then pull the player with the smoker (primary) and BOOM achievement unlocked.

The most time you spend on this will be just setting everything up which takes about 10 minutes and 5 more minutes to get the achievement, first try, guaranteed!