Just put a note on your front door:

WE RESERVE THE RIGHT TO REFUSE SERVICE TO PITAS

I always remember the story of the founding father of the firm I started out with.  He was a crusty old CPA that originally started out with the IRS and then went into private practice.  He overheard a client complaining to the secretary after the client picked up his tax return.  Crusty went out to take care of the situation.  He politely told the client, "let me see that return for a second".  The client handed it to him and he took the return, ripped it in half and then once again politely told the client "don't let the door hit you in the a$$ on the way out".  I have never had to go that extreme with a client but I always keep that story in reserve in case I ever feel the need to use that procedure.