First thing to do is to find some magazines that talk about the problems with DeBeers and diamonds in general and casually make sure that you read them together. After reading them mention how after reading that you do not think you would be able to live with yourself if you ever bought a diamond so if you ever proposed you would want to go with (insert other pretty stone here) hope that the girl agrees with you about how mean and nasty DeBeers is and wants to go with something else and lets you know what type of stone she wants.
Enjoy all the extra money you have from not buying a diamond.
http://archive.salon.com/business/feature/2000/09/27/diamonds/
http://www.mises.org/econsense/ch91.asp
http://brysonburke.com/price_debeers_cartel.html
