It is Brenda. As far as I know, all that is asked is that I give notice somehow (which can be verbal) in order for the person to know he is no longer allowed on the premises.
Also, the only other way he could avoid this law is if he were like, a paramedic, saving someone's life while freaking out about a fairly cheap CD Player.
Just issue them a notice of trespass.
The letter should state that they are no longer allowed on the premises or within the establishment and that should they re-enter, they would be arrested for trespassing.
As for this holding up in court, don't worry about that. Any verbal notice of even the shortest trespass notice is good enough to warn the customers accordingly.
Just ensure the name of the customer(s) is correct at that the letter, regardless how its written, is dated.
Here's one that's commonly used in many large Canadian retailers:
Address: _______________________________ (If Available)
TAKE NOTICE: You are hereby prohibited from entering onto, on in any way trespass upon, these premises (Company Name Here) for any reason whatsoever.
Your failure to comply with this Notice may mean that you will be apprehended for TRESPASSING and dealt with according to the law.
Dated at: _________________________________
This ______________________ Day of _______________, 2010
Issued By: __________________________________________
To finish, I would leave out your personal feelings, or attacks as they appear to be towards the customer.
Yes, they may have called you and your staff idiots, but don't overstep your bounds and become unprofessional.
Keep it simple, lay down the law and be professional. If they refuse to leave, get the police involved.