Wow, you actually went through all this for HKD 15? I hope everyone is like you including Mr. Nacho. We usually use cash or EPS when we are in HK, so we don't have the DCC issue there. We did get robbed by Ross Dress for Less in the US using our Danish credit card. I wasn't given a choice of currency (I always check the screen before signing anything) and then robbed by DCC (it was 3%) vs our bank 1%. Mr. Nacho refused to do charge back or contact Ross for it

Avis France did the automatic DCC to us too, we got a copy of our rental contract that we deliberately refused the DCC, and they still billed us the wrong currency and no refund was given (fortunately they double refunded us the wrong charge so it covered the DCC so we don't have to initate a charge back).

There are more and more places that offer DCC - not just in HKG but anywhere, sometimes you get to choose and sometimes you don't.