Funny the things you think about when throwing a sicky…
How did this ‘joke’ become so popular and is so renowned? It’s not exactly the joke that killed the Nazi’s is it! 
Because, you know, if it was, casualties would have been appaling.
Its the clever juxtaposition of chickens and roads, as well as the excitement of the actual crossing, that make this such a popular joke. It can also be seen as a metaphor for chickens, roads or crossings, all of which can themselves be metaphors.
Hey, some people think Jim Davidson is funny.