Resignations are never fun. They are often written either because of a better opportunity knocking on the door or the definitive realisation that life will remain tough and ungainly in the current environment. One can, however, make a lighter note of the whole issue by composing a funny email
Start off with customary salutations before you start taking the jibes. Describe the organisation and your stay with it in a humorous manner in the first paragraph. Use good language but do not be worried about the fact that you may sound strange.
In the next paragraph, let it loose. Let them know that you are resigning and you are glad about it. Also, let them know that the managers and the company itself is not as good as they think.
In the end, share some plans of what you wish to do with all the time that you will now have in your hand. Conclude the email with a bit of jest, it will add to the fun.