Oh, that's hilarious! I must confess ignorance as to the original - although now you've mentioned it a few wheels have been turning in my mind which make me think I may have heard it before - but you don't even need the knowledge to appreciate this, which is definitely self standing hilarity. It's probably that last line to each stanza that give it that final precious funniness, but even its precluding stuff - from the shrieking pens to the Germans to Sigmund Freud - is priceless. Oh, and the rhyming definitely helps!

Thanks for making me laugh like an idiot at midnight! :)