You can get this achievement in the flashback sequence of the game. I guess this one is
missable, so be aware of that!
There is nothing much to it, simply leave your trailer. When outside go to the left and enter the eara with the big circus tents. Go to the centre of this area and you will see a mime on stilts. use the command "pull" (or "push" I guess) to make him fall down. This will unlock the achievement!
As far as I know this is not required for the further story progression.
Please refer to minute 48 in the video below to see where and what to do ;-)
(video credit: The Killer Bits)
Hope this helps you guys!
Any improvements? Please let me know in the comments below!