Are there any legal consequences in using a fake return address to send someone a letter ONCE that pokes fun at them but isn't threatening or vulgar and doesn't ask for any money info or reply at all?

If you get caught, it is a federal offense. But I doubt you would get caught.

Put yourself in the receivers shoes - doubtful that you would want to receive such a letter. If you would not like it, chances are the other person doesn't, either.

-------------------- Recent Edit This could cause identity fraud and you haves good chance of being caught, just don't put a return address