If you don't know what you're looking at, this is just another bog standard assault rifle. If you do, well...
This joke has at least two layers. First, if you happened to watch Youtube videos by Jonathan Ferguson, Keeper of Firearms and Artillery at the Royal Armouries Museum, people trying to un-bullpup the SA80, the notorious service rifle of the British Armed Forces are something of a running joke there. This is such an attempt.
However, there's also another layer to it. At its mechanical core, the SA80 is an Armalite AR18, a weapon that was supposed to be a replacement for the fairly finicky AR15, but barely found any buyers. For better or worse, several countries purchased them for research purposes - one of them was the UK, where the bright idea was to turn it into a bullpup, and they fucked it up in the process like you wouldn't believe. And what you see here is a series of SA80 bits and bobs overlaid on a photo of AR18, with a LR300 telescoping stock because I just couldn't be bothered to warp a SA80 stock pad and cheek rest into the shape of a full stock. Plus it looks slightly cooler that way.