We had a system to censor users' IMs. Customers could configure a forbidden word list, or use a default one that had some seemingly obvious swear words. That was fine, until you realize that a global customer base has at least one person with almost any imaginable word in their names.

The North Koreans even made a phallic missile called No-dong. There is just no way to apply English assumptions about what words are across names. Oh, and the South Koreans have a town called Nodong-dong (http://www.agoda.com/city/nodong-dong-kr.html).