The day I had my horrible experience with "the clerk that hates coupons" at my local Walmart, I sent a complaint to the store via the corporate website. I strongly suggest that you formally complain when you encounter rude employees or have a negative shopping experience. Couponers are legitimate customers; the only difference is that the manufacturer is paying the store instead of us.
I'll say it again: YOU ARE NOT RIPPING OFF THE STORE BY USING COUPONS!
The assistant manager of the store called me and apologized, then offered me a gift card in the amount of the coupons the clerk refused. I need to go back to the store for canning supplies (Walmart is one of the few stores in my area that has them), so I will accept their offer. Now the store has retained a customer and, hopefully, my future experiences with them will be positive.