I'd advise getting a job at a retail store... preferably a smaller one. You'll learn to have to deal with people when they're at their worst. Plus you'll be given varied tasks and meet a lot of people from different walks of life, from retirees to students to slackers to people who have another job full-time.
Don't be too picky, but try to find a store that deals in something you like or know about.

Retail can be irritating but it definitely prepares you for dealing with people and putting up with stress.

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"It's never over... BOY!"
The Tall Man, Phantasm III