Is it bad etiquette to use a credit or debit card to pay for single figure amounts at the POS
Until the CARD act, credit card rules required that merchants had no minimum purchase requirement to use a card. New rules permit a minimum but it must be clearly posted.  Update - Stores can now refuse small credit card charges is an excellent article which clarifies the rules. It appears that these rules apply to credit, not debit cards. So to be clear - the minimum do not apply to the OP as he referenced using a debit card.  "Superiority"? Hm. I'd be a bit embarrassed to charge such small amounts. Although when cash in my wallet is very low, I may have little choice. Note, and disclaimer, I am 48, 30 years ago when I started using cards, there were no POS machines. Credit card transactions had a big device that got a card imprint and the merchant looked up to see if your card was stolen in a big book they got weekly/monthly. Times have changed, and debit cards may be faster, especially if with cash you give the cashier $5.37 for a $2.37 transaction, but the guy entered $5 already. This often takes a manager to clear up.