Retail is a fucked up vicious cycle of endless dumbasses who get what the want. They yell and yell and eventually learn that this 'yelling' is the way to get what they want so they just keep doing it. They don't even try to try anything else. Grown ass adults, these people are grown ass men and women throwing temper tantrums to get what they want because of the horrible injustice being served to them.
I think everyone in the world should have to work in retail as their first job so they can learn the horror of customer service and hopefully kick this stupid habit.