lets just go ahead and use common sense here and say that the owners could refuse to serve them IF they are creating a disturbance or bothering other customers with their attire. just like it is now.
Last time I checked, if a customer comes into a private business and insults staff or causes problems they can be escorted out by the cops if they don't leave. If you own a business you can refuse service to people...worked at restaurants for years, lots of people who are not allowed in for causing problems.