If you make financial decisions based on what other people will think, you are being influenced by peer pressure. Getting a new car because your friends make fun of your clunker, buying a new TV because someone mentioned that you don't have a flat panel yet, and buying new clothes to try to fit in better with your friends are all examples of peer pressure. Many financial problems that people find themselves in can be traced directly back to giving in to peer pressure.
Most people think of peer pressure as something that occurs to teenagers. He can be very helpful to recognize that their pressure is just as prevalent in adults. The only difference as adults don't have someone else pointing out when they are succumbing to peer pressure.