How? I am not much a star wars fan, so I might not get the joke.
Well in this case, I was thinking that viewers might find it funny that heavily armored stormtroopers repeatedly get their heads handed to them in gun battles despite the fact that they usually outnumber and outgun Han, Luke, and the other guys.
Even though I was only seven when The New Hope originally was released, and took it completely seriously THEN, Whenever I see the movies now, more and more often, I see the funny side.
Looking at it that way, the armor serves no purpose at all.