Join in Singleplayer server ( You must be in Singleplayer server in order to work ! ) Open your chat with Y or U . Type "bloxwich" . ( Without quotes ) If that doesn't work for you, it might be for the following reasons... You already have the achievement . You got the achievement , but it didn't pop-up . You're in Multiplayer server . *edited
But why exactly "bloxwich" ? Bloxwich is a market town in England where Garry Newman ( Developer of the Garry's Mode ) has been born . It's probably a Easter egg .
Join in Singleplayer server ( You must be in Singleplayer server in order to work ! ) Open you chat with Y or U . Type "bloxwich" . ( Without quotes ) If that doesn't work for you, it might be for the following reasons... You already have the achievement . You got the achievement , but it didn't pop-up . You're in Multiplayer server .
Actually I'm pretty sure this works in multiplayer too. IIRC when I got it I was told to by someone on a server