Wow.
its not in the employees job description to clean up entire aisle of mess due to angry customers. For the most part, your average bagging clerk / checkout clerk is being paid minimum wage.
Your attempt at a "demonstration" is only going to make them do the extra work of having to take all those groceries you took to the register, BACK to the store shelves and restock them. Potentially reverse an entire transaction, and any responsibility that the store owner is likely to dump on their lap for you refusing the sale.
Don't be a dick. Seriously. A childish act like that isn't even targetting the right people. The Store clerk has absolutely zero say over what payment options are accepted. They're not going to be able to change anything or even help you get what you want.
If you want to voice your concern that you wish to use your payment of choice. Don't shop there, write them a letter, Complain to their sponsors / suppliers.
Being a dick isn't making a statement other than you're a petulant twit who wants to throw a temper tantrum like a 4 year old.