I can't fault those who choose not to because of the reactions. It's a bummer you are in a state that unconstitutionally made it illegal for so long that people don't realize it is supposed to be normal. I live in Nevada, where it has never been illegal, and while it went through a period where it was more rare, it never really went away before the resurgence. I've been doing it for 22 years and it's nice to see more and more.
Honestly, if I lived in Oklahoma, I don't know if I'd do it everywhere, either, if it became an issue. Only once, and recently, was I asked to leave a place in Nevada, and that was because of a rogue bartender who didn't know his corporate policy. It was corrected expediently.
As for a clerk that did something so horribly stupid as to feign panic, I would not let that slide. As you noted, that is so dangerous as to get you mistaken and possibly killed in someone's reaction. I would have had it corrected on the spot, and if attitudes didn't allow it, I would look into his employer or seeing about filing charges of disturbing the peace.
As with all civil rights movements, it requires lots of steam to pull away from a dead start when you haven't had the benefit of two centuries of inertia like the freer states. And like with other civil rights movements, there will be a lot more talk than action, especially when it comes to the civil rights of people that just want to be left alone in the first place.