Before we get to the ironic part, we have to know – what does invisible spray do? Is it supposed to make objects invisible? That’s pretty amazing. On the other hand, if it’s just called “invisible spray” because the spray is invisible, it’s not as impressive. Either way, we’ll never find out, because you can’t even see the bottle. Invisible indeed.
We realize the shelf is empty since the product is out of stock (who wouldn’t buy “invisible spray”?), but this wouldn’t have been funny if it was any other product. We don’t need to explain the joke any further, we’ll just let you enjoy it.