Even though you where ... are 100% correct about our rights and its legal here in the state, you have to be a bit more "tactful". Here are some examples to use next time (hey i had to learn too)
* Explain the reason why you have a firearm/ "emergency tool" is for the fact you have a licence for it/ CCW and in that county its legal to have it OC with a CCW. Maybe explain how in in Missouri, that a; knife, baton, etc carries the same punishment as a gun and with proper license its legal to have (even though its legal in the state, but in many areas as we know of you need a CCW... remember, you have the information and if you can explain it well... 99% of the time they will go what you have said vs. Now the manager is going to report it, make a sign and try to get a promtion of keep people like us out)
* Be humble (not a wuzz), its their company/ business and we are asking to shop there. Its just like the rules; no shirt, shoes, no service. Its basially falls into that area of the law. For many, they believe since almost anyone can buy a gun then there is no regulation on who can carry it. they may have viewed you as a teenager who went and took their daddy's gun and now walking around with it. Plus the casher was the true "trouble" instead of talking to you about it, they reported it and a manager is going to "protect" their "flock".
* Follow up with a written letter to the company about what happen. Its always best to have two sides of the story. For example, I made a formal complant to Starbucks about two weeks ago about the same thing. What came out of it is this... Corporate will follow the local laws on OC. If its ok at that city, then its ok at that store. BUT... the manager may view it differently and wish to add their own rules.
Just think first, prepare of the "what if's". After all, if you paint the picture in their head that its more than just "our rights" and that a number of people shop there, once a sign is up that many people will stop shopping there. Afterall, its business... policies changes quicker than the city's.