People who work in retail have it bad enough. Don't treat them like garbage.
As somebody who's worked in retail (from shoe stores to specialized departments), I can tell you it's not easy. Juggling classes and working hours that cut into study and rest time make life hard enough as is, but my books aren't going to pay for themselves.
That being said, there are many, many people who come by and act so entitled because they want you to help them with something, so I guess they see it as you being their servant of sorts. They come in with an agenda and just dump it on you.
For example, people who come in looking for an item at the end of back-to-school week when it's already sold out should realize that it's sold out. I'm sorry to be the person to tell you the truth, but I can't magically give it to you. So don't be like that guy who yelled at me because "I don't give a shit about exhausted parents." Listen, I feel for you. But don't be the umpteenth person who gets pissed at me because you put off getting something until it was too late. Don't literally throw your box of printed business cards at me when I warned you they would be low quality because of the resolution and you said it would be fine.
If there is a long line, don't be the person to take it out on the poor cashiers. They're trying their best. They have other things to worry about. Don't be a jerk.
I understand some people who work in retail can be rude. Just tell their manager if that's the case. But in many of the places I have worked, I was always as polite and helpful as I could humanly be. Many people are nice. But there are quite a few that just dump their problems on you.
Talk with your family and friends. I'm not going to sit here listening to you yell at me for waiting so long in line while you hold up the very same line. Take that out some other way. Meditate for 20 minutes a day or something. Don't bring that bad mojo in here.
Re-evaluate how you treat people. Don't bite the helping hand. Don't be a jerk.