A thug who affects roughness, partakes in crime, and hangs out with others in his gang. The purpose of his behaviour and affected image is to make him feared and powerful, and to earn him respect from his peers who are also involved in crime. He typically has a specific dress code, social code, and vernacular to identify him with his gang. Moreover, he often relies on drugs to induce or augment his rash behaviour. He is, in short, a feared idiot.
The word "gangsta" is also used by clowns who imitate real gangstas and who are equally stupid.
Yo' know who I am? I am a gangsta, fool. Give me all yo' money, mothafucker! I don't have brains. I rely on my thuggish behaviour to make myself feel important.