Is the barber doing it for you, or for the washtowel? It seems that you are the customer, and if you want your hair shaved off, then that's what you should be getting. Never mind checking with joke-hova or the Filthful and Disgraceful Slavebugger before giving the customer what he wants--especially when such is reasonably possible, and the directive is clear.
Or, maybe it's time to find a barber that is not a jokehovian and tell this one that, unless he complies with your wishes and not the Filthful and Disgraceful Slavebugger, he will lose a customer and possibly others. Or, you can get a grooming tool that will let you shave your own hair (they also allow you to cut your hair quite short) without any interference. Best part--once you pay for the tool, you start saving money on barber's costs and you get to do it on your schedule, not just when they are open.