Want to invent a new language but not in a rush to finish it?

If you and your friends started making up new words or words to replace common words, and just used them until the group understood them. And if you gave each other high fives each time a new word was used, the positive feedback would increase new word recall. So if you did this at an average rate of one new word every week, within a few years, those not in the group would struggle to understand your secret code. And in 20 years, you would pretty much be speaking a whole new language.