|Yes, I am the real Garry!|
This achievement involves connecting to the same server as Garry Newman. This achievement is much known as a troll by Garry as he doesn't play Garry's Mod anymore.
On December 31, 2015, there was an exploit that made it possible for people to appear as Garry and give everyone on the server the 'Yes, I am the real Garry!' achievement. This was fixed in the 2016.01.18 update and the achievement become impossible again. However some people have claimed to have obtained the achievement even after Garry stopped playing AND after the bug was patched. On March 4, 2018, an achievement hunting group called 100Pals hosted an event with Garry, in which a user contacted him via email and he agreed to help them. About 443 users got the achievement that day, and a video of the entire event was recorded and uploaded to YouTube by the user who got in contact with him.
Why it's nearly impossible for late comming players Edit
Garry has quit GMOD and is now developing other games such as the new gmod.
Garry himself cannot get this achievement. #GarryCeption
Before the second achievement update, this achievement was named "Are you the real Garry?"
The achievement icon represents a cog, which implies "connection" to a server or "connection" to somebody.
Nobody knows why, in the 2015 update, did looking like Garry count as getting the achievement, and why the achievement has still not been cut from the achievement list despite Garry quitting playing Garry's Mod.
There is only one possible way of getting the achievement now, and it is hacking.
(No longer valid. Event ended March 4th, 2018.) Last chance to get the achievement: https://nm.reddit.com/r/steamachievements/comments/7zfwos/gmod_one_night_only_garry_newman_march_4_2018/