Fer Booyakasha mean a right many fings. But like fer da most part its a greetin innit. Iz use it all da time wit me posse.An When Me iz nobbin J Lo. straight up me aignt shitin you. Yo shout out bredren. Iz out Frek mez, Flamez.
Actually, since Ali G is Jewish and comes from Israel it means something totally different. In Hebrew there's a world called BEVAKASHA - which means 'Here you go' basically. So he made it into BOOYAKASHA.
1. a quick exclamation used when one has owned, pwned, shanked, kicked the crap out of, or mentally abused someone followed immediately by a quick snap of the fingers.