I first this book about 20 years ago, and it has returned to me in my mind (okay, I don't want to get too psycho-analytical here) again and again. The reason is this: it reveals a secret. I have often heard people say stuff like - 'we've got a different sense of humor', or 'jokes are specific to culture' or 'how can you find that funny' - all without any explanation. I mean - if I see a rubbish car, I can usually explain why it is rubbish by saying it's engine is weak or it has no lights etc... but with jokes - they are difficult to quantify and difficult to say why one works and another does not.
Das ist nicht recht, as Freud might have said. Here he basically provides a formula for what a joke is. Therefore, if a joke does not meet a certain set of criteria, then it is not funny. It forces you to take a joke apart, look at its elements and see if it is actually a joke or not. The key to the way Freud worked this out is in the title, that is, if a joke does not relate to the unconscious - those unsaid things we all take for granted, usually in everyday life, then it can't be funny. For example, I am an alien and on my planet, all gaboobas carry shanimas for cultural reasons, which are actually too big for them, although no-one has ever realized or pointed it out. Then I deliver my alien punchline: 'Today I saw a shanima carrying a gabooba to work!!!' Get it? No - exactly, it is not funny (unless you are French which is a whole different matter and none of this applies to you).
Anyway, this book is a sort of light-hearted intellectual read, interesting after having watched or read some great comedy. I definitely recommend it as a way into Freud or if you are over-familiar with the babies and their potties and dream analysis.