Even though Rappers were mentioned in this set of posts no one addressed the fact the use of "don't" instead of "doesn't" is common African American English (AAE is sometimes called Ebonics). AAE is very common in lyrics written by African American artists and by many imitating thier style (such as the Beatles who admitted being strongly influended by African American blues artists). Here is a link (one of many) if you're interested in AAE:
http://www.cal.org/topics/dialects/aae.html
Joel