Just right click on your game in your library and choose Properties. Then, go to DLC tab and see if you have checked Left 4 Dead 2 - Christmas 2013. If so, people who are playing with you can earn this achievement and you cannot, if not - you can get this achievement, so simply uncheck it. Done!

Information from user "Psycho Werekitsune" - you don't have to survive the campaign and you don't even have to play it from beginning - only "free holiday player" must survive.

IF YOU DON'T SEE THIS DLC, IT MEANS YOU HAVE FULL PAID VERSION OF A GAME AND YOU ARE ABLE TO GET THIS ACHIEVEMENT REGARDLESS. Just play with someone who has this DLC AND DON'T HAVE THIS ACHIEVEMENT - person like this is pretty hard to find, so the best idea is to create a new Steam account and share your main account library with it (if you have L4D2 with this DLC).

IMPORTANT INFO: It seems that you have to play campaign from beginning now - when player who wants this achievement join campaign in other chapter, (s)he won't get Good Guy Nick.