A certain type of douchebag that lives in the New York City metro and is usually of Italian descent (although in my town, some of the Guido-types are Irish, Jewish, Hispanic, or Eastern Europea in addition to Italian.) You can find him in Brooklyn, in Westchester, the Bronx, Long Island, New Jersey, Staten Island, etc.
They are known for driving fast, tricked-out cars like BMW's, with which they blast their God-awful techno music.
They can be spotted wearing spiked-up hair smothered in gel, and often go out for fake tans.
They sport clothes such as A|X (an alternative, Politically-correct term for Guidos in my town is "A|X kids.") They also wear wife-beaters (they're behavior mirrors the name of those clothes.)
They also carry around Nextels that make the awful chirping noises.
They are generally all-around assholes who smoke pot, drink, harass people, live frivilously off of their wealthy or middle class parents, and trash people's property.
"I just heard a Nextel, must be the Guidos again."
"Those Guidos were blasting their crappying techno by my house last night."