Very thought provoking thread.
It is important I think to know if this is actually true.
I say this because I would imagine that if I had tourettes, the last place I would want to work would be in customer services dealing time after time with people who did not know me and werent aware I had a verbal tic.
If we believe this situation hundreds of times a day this woman will be looking up into shocked and upset faces, all day every day, hoping presumably that people grasp the situation and dont react in a hostile manner. You might I suppose get away with it in M and S but front line customer services often involves defusing situations with angry customers and I second the concern that she might end up being verbally or physically abused. And no I dont think she would be dealing with the same sort of reaction if she was for instance, a wheelchair user.
It is the social inappropriatness of the verbal tic that is the issue in this situation. We do not as a society, swear at paying customers, so we do not as paying customers expect to be sworn at. People reacting in unexpected ways makes us very uncomfortable, and for good reason, if social interactions do not go the way we expect, it is slightly frightening because we dont know what will happen next. If you have time to know that person this ceases to be an issue, but in customer services this is clearly not an option.
Why would you, given this particular tic, not prefer to work in a situation were your coworkers knew you and your verbal tic was forgotten, and ceased in fact to be a disability because it would cease to be a factor in how well you did you job. If any of us were asked to describe good customer service it would based on polite friendly interaction- all you have to go on in a short interaction like paying for clothes. Shouting obsenities does not result in a polite friendly interaction, it is a shocking uncomfortable situation, because it is unexpected from someone working a till
It seems so unlikely to me that a store would think this was the best place to use this woman's skills or that some one with tourettes would chose this position.