Work complaints

I'm obviously not gonna say where my job is but it is fast food. Let me ask WHY are people so up tight and NEED to just complain and see how far they can go until we give in for whatever it is that they want. I had a guy come right when we closed and was mad that we couldn't add a specific fruit for him. I checked the time and he actually spent almost 20 minuets to try his best to get it his way after again us being closed. IN THE END HE IN FACT DID NOT get it his way yet still tried to complain even after he gave up. I just don't get it. We are paid minimum wage sir I really do not care for you THAT much and don't get paid enough to bow down to you. ;_;