Of course it's a douchey move. It's an appropriately douchey response to a douchey manoeuvre by the company.
And they'll complain to their boss, and they'll complain to their boss, and so forth. This is how things get fixed - from the grassroots level. Enough people do it and there'll be an obvious monetary penalty to the company. Until they're negatively impacted, they won't give a crap about the customer.
So your plan to combat their douchey move is to be an even bigger douche?
That's not going to accomplish anything. There's no way a casher is going to go to bat for you with their manager after you treat them that way. You'll just become that customer and they'll most likely remove you from the store and refuse to listen to you.
Somehow I don't think you thought your cunning plan through...