I agree that appearance matters. It is the first way you are judged by others. That doesn’t excuse disparate treatment but it helps to explain it.I think you are thinking there is protection under the law and through the courts for things that are not protected such as your sexuality. If your demeanor conveys you as you've described yourself, bisexual and rather gender fluid in appearance, more particularly if you happen to have ink and piercings and dress very non traditionally, you have probably experienced quite a bit of this type of negative attention in any of the small towns where this store is located. It would be a beautiful world if it wasn't so, but it's the reality of what happens.
And if you, looking this way, came into a store in this place and began going through the merchandise at a very slow pace, making pictures, etc. and stayed for a considerable length of time, you were, and you know you were, jacking with the store staff. It may have been what you wanted to do, but you don't get to do it without taking into consideration that they're going to react in a certain way. And it's not illegal.