Bahhaha, oh if I ran this store, Head Office would be sending me e-mails about customer complaints everyday,

Actually, maybe less. I think I handle people well.
Now, an update on my letter. Sadly, we won't be sending it. We've decided to give him the ability to come back to our store with the credit, given the possibility of apologizing (a very rare event), and if he doesn't, we'll ban him in person. I suppose it saves us on postage.
What I did do though was place signs around the store explaining the Banning procedures, laws, and a general notice of "We don't have to serve you". I don't have the writing with me, I re-wrote it at work and left the hard copy there. It's not that interesting anyway - but it's fairly clear and explicit. If you're rude, your gone. We don't need your money. There's plenty of nice people wiling to buy our $597 42" TV's and $279 2500 PSI Air Compressors...