I've worked several retail jobs in my short 20 years of life. I spent two years working at a grocery store, I've dabbled in the restaurant business, I worked at an ice cream shop (which I'm returning to this summer), and I currently work at a private gym. I've pretty much seen it all.
The number one thing these jobs all had in common was how horribly some people treated my coworkers and me.
You would not believe the incredibly terrible things that have been said to me or about me by customers at my job. At the grocery store, one lady called me a b*tch because she couldn't buy something on food stamps (I don't make the rules, sorry?). At my ice cream store, my best friend had to call the police because she refused to give a refund to people who had already eaten half of their ice cream and refused to leave her alone. A friend of mine at the gym has been yelled at by a fully grown man because she locked the door when she was supposed to.
Those are just some of the key incidents that come to mind. There have been several less severe instances of mistreatment in my career in retail.
Working retail jobs will definitely harden your skin and humble you. You have to learn how to brush off the rude people and maintain the smile you're required to have at work. You can't let one person's sour attitude ruin your day, and that's something that can be applied to your life as a whole, too: don't let one sour person ruin your positivity.
Always remember that we're all human. If I wasn't here checking you in at the gym or serving you ice cream, no one would be here to do it. You'd have to do it yourself. Be respectful of those who do the jobs you wouldn't want to do, and need to exist to maintain your lifestyle.
I am as nice as can be to every retail worker I encounter off the clock, because I know very well that one smiling customer can make your day just a little better. I treat everyone I encounter as my equal, not as though they're less than me, because I know how degrading it feels to work in retail sometimes.
Be kind to others, always. That's the biggest takeaway I've gotten from retail work.