"We teach other people how to treat us," notes human behavior expert Patrick Wanis, Ph.D., on his personal website. When you're dealing with people who are selfish, make certain to speak up for yourself as soon as the person begins to step on your toes. For example, if your spoiled nephew, who is 22 years old but acts 15, decides that stopping by your house every day to raid your refrigerator after work is preferable to buying his own groceries, tell him you need him to stop by the store and buy milk and sandwich meat on his way over tomorrow. If you don't allow people to behave selfishly, they can't.

If you've given a selfish and spoiled person the opportunity to change her behavior, and she chooses not to, walk away from the situation -- figuratively, if not literally. This is easier when you're dealing with a friend or acquaintance, but it can work with family members and coworkers, as well. For example, if your spoiled sister-in-law never bothers to write thank-you notes for the gifts you give her and her family, stop spending your hard-earned money on presents. When a colleague wants to waste your time yet again whining about how difficult a project is, excuse yourself and leave the room.

Don't feed the selfish person's sense of self-importance, advises psychologist Roya Rad, Psy.D., in a "Huffington Post" article. Stay true to yourself. If you wouldn't ordinarily acquiesce to someone's demand to always choose the restaurant you go to, don't do so when your best friend's semi-famous cousin is in town for the week. Entitled people can be very persuasive, and if you're not careful, you can be fooled into somehow thinking they're deserving of special treatment. Stick to your guns, though, and only let such a person get away with what you're willing to give.

Be patient, advises Rad, noting that selfish people have often had past experiences that have resulted in them using dysfunctional self-protection strategies. Instead of despising the spoiled and selfish people in your life, try to view them with compassion. Continue to hold them accountable, but don't allow their aggravating behaviors to inspire you to behave in ways you ordinarily would not. For example, if the self-centered neighbor in the apartment next to you insists on blasting music at 3 a.m., go through the proper channels to address the problem rather than purchasing a yippy Chihuahua in retaliation.