Left 4 Dead 2

What i recommend is play scavenge mode and wait till your a spitter and stay in spawn mode untill a smoker spawns. Stay near the smoker and he'll probably pull someone. When he pulls that person and starts smacking him spit on the survivor hes pulling. Just do that and this cheeve is yours.

* I said scavenge because the survivors tend to split up more often*

With the new update that was released on 4/20/10 this achievement can be earned in Scavenge mode by yourself as long as you have 2 controllers. With the new update there can now be more than 1 special infected. Here's how I did it:

IMPORTANT NOTE: once you spawn the spitter at the start of the match and if you don't get the achievement on the first try just hit rematch at the end of the match and you'll spawn they spitter every time at least that's what happened for me.

Start up a scavenge game on Dead Center in the atrium. main account as infected, 2nd controller as a human. Restart until you spawn as the Spitter, set up your spitter on the stairs on the right from the starting point 2nd or 3rd floor standing on the railing. You should be out of view from the survivors.

Then as the survivor go grab that gas can then go wait towards the left rear of the car, kind of by a pillar as well. Keep an eye out for the smoker with your spitter, they will be highlighted in blue kind of helps to have full subtitles on. When the smoker pulls someone in try and spit on them. You may have to wait for a 2nd or 3rd Smoker.

here's what you should do: try to get one survivor far from the group and let a smoker pull them until they take damage from choking, then spit at the survivor and there! You got the achievement