Younger males (and for some unknown reason, a couple slutty females) who create a certain image for themselves. By wearing oversized clothing and shoes, walking with a swag (usually because their pants are falling off) and mutilating the English language every step of the way, they believe they acquire "street cred".
The sad reality is that these people have never seen anything scarier than their momma's bra, or their own faces in the mirror. They congregate with like-minded individuals hoping to intimidate. Very few of them are actually affiliated with something criminally-inclined, such as petty theft.
See, there's two types of "Gangsta's".
Type one is the originals, the old school freaks with high morals. You don't fuck with these, but they usually won't start with you. They take part in organized crime, and try and better the community. These are Gangsters, the actual kind, and they'll never go around yelling they'll "pop a cap in yo' ass" - they'll just pull out an AK and mow you down, silently, without emotion. They're usually very, very patient people though.
Type two: Gangsta. Yo WORD UP G! We've all seen these G-unit clowns who form a "gang" with their gangbanger faggot friends and go around trying to prove something. They need to be reassured every step of the way that they are indeed Gangsta and tough.
They steal candybars, wallets and the occasional cellphone. They might, after 10 years, get one gun and two bullets for the entire gang, then shoot some punk just to prove they can. Low-lives is too grand a term for these fags. Best part is, not a single one of them can fight for shit.
1) See that guy's briefcase? There's a fucking smg in there, that's a fact. See how he's wearing a suit though, and not running his mouth? That's a real gangsta.
2) Check out that fag in baggy clothes! Thinks he's gangsta, but can't even stop spitting when he talks. Let's trip that bitch down the stairs.
3) Yo word up gee. We gangsta, aight? Aight? Aw jeez hide the bandanas my mom's coming.