I want to dress up as a police officer and shake people down for cash and pharmaceuticals.
That does not sound good. What makes you think you'd be allowed to impersonate a police officer for money?
Because I want to do it for fun
False representation as an officer is completely illegal, no matter the context. Try to make money using more legitimate means that won't get you arrested.
I'm going to do it like it is just a joke. I think I will get away with it.
I think it is dangerous to pretend to be a cop. What if somebody thinks your disguise is real and hurts you.