I don't know who this script is talking about. Is it about Mike or is it about Oozma Kappa?
The phrase "go crazy" here is being used to as an invitation/request to proceed with a requested action. It can also be used to mean that you should have fun doing something. So it is directed at Mike here as the character is telling him to go ahead and join the Oozma Kappa and that he should have fun while doing so. Ex: A. Can I eat some of this pizza? B. Go crazy.