The Uninfected Trophy in Aliens vs. Predator
Finish a Ranked Infestation match as the only remaining prey
How to unlock The Uninfected
This can be simple so long as you know how to play this game mode. All you have to do is wait around/run around the map surviving. You need all the other players you are with to get infected by another alien. You can see how many aliens to marines there are on the left of the screen, the blue symbols are for the marines and the green are for the aliens. So as others get infected the symbols will change to green, an announcement will then state 'Last Man Standing', obviously it needs to be you for this to work. HOWEVER, this is not the end. You now need to survive by yourself for a further 30 seconds, when the timer hits 0 the game will end and you will earn the trophy.
Boosting this is difficult since you can't join a game of Infestation as a group, everyone has to join separately but due to bad coding there are region issues to contend with. There issues mean you have to be in roughly the same country as your boosting buddies to stand any chance of being matched up with them.