Well, it's too hard to endure and wait, but if you will unlock it legitimately, then nothing will happen on your account. So I recommend you not to use the SAM (Steam Achievement Manager) (or any third-party pass which will unlock the achievement). If you use it, you're status will be screwed. Better to wait the right opportunity than be disappointed because you are going to ruin your account/stats if you use cheat to unlock it.

The Good Guy Nick achievement has been started on October 25th to 29th, 2012. It was the Halloween season and lasted for couple of weeks.

After the Halloween season, there are another timeline that GG Nick occured:

• July 4, 2013 (1 day)
  
• May 2018 (4 days)
  
• May 2019 (4 days)
  
• September 2020 (3 days)
  
• July 2022 (3 days)
  
• November 14 to 17 (15 to 18 on some countries), 2024 (4 days)

This was the Independence Day event.

First Spring Cleaning event.

Second Spring Cleaning event.

The Last Stand update event. The major update on the game where they have different changes in gameplay.

A charity event hosted by WaifuRuns for Suicide Prevention Charity.

Fifteen year celebration for L4D2.

This GG Nick is rarest to achieve because it's seasonal achievement. You need to follow the following:

You need to find a player who becoming a "Nick"—an account which they haven't bought the game (on this case, my alt haven't bought the game, but kept it for free in order to help). Then join at their lobby.

In lobby, you can ask first a players who is Free Weekend player (can help you to get GG Nick). In order to verify it, check their Steam ID and check if they have other games which are playing. Sometimes, their games they're playing haven't show, so better to find people who haven't get GG Nick yet because they might be Free Weekend players.

If you're host, better to set on Crash Course because it is the shortest map. If you're joining, ask politely to the FW player to set into Crash Course.

When you're in-game, make sure the FW player is alive and not dead until the finale of the game.

Don't leave yet after the game, wait for the credits to roll out in order to get the achievement.

No, unfortunately I can't help you here at main account, but I have an alt account if you want to achieve it. We need to wait again for GG Nick. :)

Add me here at my alt! If you help me to survive in the entire campaign, and you wait for the credits, you'll instantly achieve it. :) Also, please leave a comment that if you don't have achievement so I can host a game where you'll join with me.

If I'm not available, you can join the group Good Guy Nicks! Mods and admins are willing to help you to get the achievement!

Here are some FAQs on GG Nick...

Answer: No. You need to wait for Free Weekend to occur. If there's a Free Weekend, GG Nick can be obtained as long as the Free Weekend player survives the whole campaign. You can see the status on Store Page if it is free or not.

Answer: No. You can play any character you like.

Answer: No. You can play any campaign you like, but I recommend it to play on easy difficulty. Also, it's good to play in the shortest campaign, which is Crash Course because it has only two chapters.

Answer: Yes! As long as the free weekend player has no death yet and survives, you can still obtain it. You just wait for the message to appear.

Answer: No, you'll be come a “good guy”, too. Also, it might null the achievement since you haven't bought the game.