Card envy can turn reasonable people into snarling, raging jungle beasts.

After I got a Centurion card two or three years ago, my sister wanted to know everything about the card. She said it made me better looking, taller, thinner and all of these young women seemed to be interested in me.

Let me tell you about my sister. She is 52 years old, owns a very successful business in the Mid-Atlantic area, but her Amex bills topped out at $200K annually. She is also the point person taking care of our aging parents (mom has severe dementia and dad has too many health issues to discuss here) and is doing a great job.

So, my sister has started taking more short trips to decompress from the issues of my parents and life in general. She dropped a few hints about the card and my concierge got some restaurant reservations and tickets for her, as a thank you.

One Monday a few months ago, after a trip to NYC, came the phone call - "I want a Black Card. Now." So, after making sure that my wife would not have a fit, my sister became an AU on my account. She says that she is the source of Card Envy among her friends, clients and business associates.

So, there you go. Sibling rivalry can turn into card envy, which can turn into an Authorized User.