I insist that I don't find that joke funny. Really, it's just stupid. But for some reason I laughed for three seconds when I got to this bit:

but you have an orange for a head. How did that happen?"

Then for about 20 seconds when I got to this part:

"For my third wish -- and, this is the bit where I kinda fucked up -- I asked for an orange for a head."

Then, when I went back to find those two quotes I laughed for another 3 then 5 seconds. I also laughed three more times while writing the text of my reply.

Because he wished for an orange for a head. That's fucked up.