A tired meme at the Something Awful forums (and perhaps elsewhere on the internet). Initially it was the funny concluding line of a joke; since then, it has been broadened to be used as a corny punchline for other jokes, and has broadened even further to be added as an addendum to message board posts FOR NO BLOODY REASON (as parasitic memes tend to do)

When you eat dirt for the first time and leave your family to build a shack in the woods