This happens so often, I work in a Woolworths bottle shop.
Customer: Do you price match the wine? Since I saw this downstairs for $10 and in here it's $14.
Me: No sorry, we don't price match, you could get another one or-
Customer: People like you are the reason everything is so expensive! It sickens me you can charge so much more than the other stores.
Me: Sorry, I have no control over the prices, I am just working here.
Customer: Yeah, I'm sure, well you should change it or price match for me.
Me: Why don't you just go downstairs and buy it?
-Customer storms off-
The other bottle shop is literally 20 metres away.
Me: Can I see I.D?
Customer: Yeah, I'm 20 I just left my I.D in the car.
Me: Well, you will have to go get it mate, I can get in trouble if they see I didn't check you.
Customer: WHAT THE FUCK I AM 20 AND I COME IN HERE AND YOU WANT TO CHECK MY I.D! DO I LOOK 16 TO YOU?
Me: Sorry, but I could say that I'm the king of England, but that doesn't mean it's true, so either go somewhere else or go get your I.D.
Or.. Just people generally threatening you because they are really drunk and you can't serve them..