This is the best piece of wisdom I've learned in my first year out of college in the "real world":

There are idiots in every field and at every age.

To elaborate: When you're younger, you think that when you get older, everyone will be nicer, smarter, more capable, and more mature. This is almost entirely wrong. People with extreme personalities (especially negative ones) will generally calm down in their early 20's, but for the most part, you get the same groups of people at all stages in life. There's always the rich kids, smart kids, dumb kids, bullies, attention whores, ultracompetitive freaks, etc. at all stages in life - they don't magically change or go away (although the extreme substance abusers tend to die early, and the bullies calm down, usually from substance abuse or imprisonment).

Furthermore, people's jobs and academic qualifications do not generally imply infallibility, and they have only a loose correlation with general intelligence. Sure, there are many idiot fast-food and retail workers. But there are also a lot of idiot doctors, scientists, professors, and executives. Not everyone finishes medical school at the top of the class.

Use this information to your advantage. Never assume authority of information based solely on the age or occupation of its source, and learn to deal with idiots and members of the other social groups that you hated when you were growing up. They're simply a part of life.

And if you're particularly clever, you can even find a way to make a lot of money from them.