Woo woo woo is not to be mistaken for Homer Simpson's exuberant "woo hoo", nor is it to be mistaken for the joyous hooting that goes on in the presence of strippers or go-go dancers.
Woo woo woo is the ghetto equivalent of "yadda yadda yadda" or "blah blah blah". Sometimes woo woo woo is used interchangeably with the phrase "whatevah whatevah". According to this entry from Urban Dictionary it originated in Chicago:
Woo-woo-woo was made in Chi-Town (aka Chicago) and used by G.D. members. Woo-woo-woo takes place as blah blah blah/and so on/etc.
Jose was talkin all this shit and saying, "Oh you shady,you stupid, woo woo woo..." it was messed up.
The first time I heard it was in 2002, during an armed robbery investigation. The offender, a 16 year old black kid, was explaining how he'd picked our victim, an addled 15 year old white kid who wanted to buy some weed and instead got robbed of $50. Our offender, who was not from anywhere close to our town, explained that he came to our mall to look for a likely target because "no offense, but white people is stupid and all, you know, woo woo woo."
Since then I've heard it from a wide variety of downwardly-mobile young people of all races and ethnic backgrounds, ranging in age from 13 to 26.
I wish I had a way to demonstrate the proper body language and hand gestures that accompany this phrase, but I don't.
On a final note, the phrase woo woo woo has nothing at all to do with beloved Chicago Cubs fan Ronnie "Woo Woo" Wickers: