I've often said that everyone should spend a couple of shifts working in retail, because then they'd see how their fellow humans behave from the other side of the counter.
I think most people truly don't realize what tremendous assholes and bitches they are. They just think they have wants and because the person behind the counter is being paid a whole $6.50 an hour, that means they are being compensated for taking their shit.
Practically no job in the world compensates a person for the amount of shit they actually take or deal with, and it seems like a lot of people demand the sun, moon, and stars for that $6.50 an hour. Yes, many people who work those $6.50/hour jobs are total morons and that's WHY they are in that job, but that's hardly all of them. Even still, the yelling and screaming idiots i've seen in my time are, by and large, yelling and screaming like idiots because of their own issues, not because the person helping them has actually done something to cause it.
For me personally, I've been in commission sales and at a management level in that capacity, and I took a lot of shit. Thankfully, when it comes to person-to-person confrontation, I'm cool as a cucumber and maintain a constant smile. it tends to piss people off way more when their yelling and screaming results in absolutely no change in your positive and polite tone of voice, and smile.
One time a guy was in my face, almost touching me he was puffed up so close to me, and telling me how I was an asshole and "stupid moron idiot" and was telling me off for standing there smiling at him. His friend, who had been standing well back in silence, finally grabs him by the shoulder and says, "you DO realize that RIGHT NOW, you're yelling at this guy for SMILING, right?"
It was a small enough store that anyone in it was within earshot of everything said, and the 10 or so people in there at the time all started laughing. The guy looked at the laughing people and stormed out. SO satisfying.
(PS he was pissed because he tossed his cellphone out of the window of his car while traveling down a highway [you'd be shocked to know how often people do that, btw]... and he was honestly surprised to find out that the few pieces he want back and retrieved would not be swapped out for a new phone)