The latest urban slang word in the groovy-cool-bad-dope-phat tradition (meaning very good, excellent) is "crunk." In classic slang tradition, crunk can also mean the exact opposite -- extremely bad. The key is that it is extreme.

As for its origin, the rumor I have heard several places is that it originated with "syrup heads" in the Houston area. Syrup heads are a subset of drug users who get high off prescription cough syrup with codeine -- it is drunk straight up, mixed with alcohol, or used to coat "fry sticks", which are joints laced with embalming fluid. (What will those crazy kids think up next. Yikes.)

I offer up the following from a site with the title "So you typed 'crunk' into Google..."

Indisputably Crunk

There is some crunkness that cannot be denied:

Actor Sterling Hayden, clowns, anything having to do with the
genitals, spandex leggings worn outside a gym, singer/actress
Courtney Love, halitosis, Las Vegas, Eminem not winning the
Grammy, crackheads, drivers who fail to use turn signals, new car
smell, cloning.

Not Typically Crunk

Think 'banal.' Items on this list are unlikely to be crunk in any situation:

Public telephones, Scotch tape, local newscasters, the cardboard
inside a package of stockings, TGIFriday's waitstaff, "Marmaduke,"
ordering from a catalog, lint, iceberg lettuce, ceiling fans, "People"
magazine.

In looking for a definition of crunk I was thrilled to find The Rap Dictionary at http://www.rapdict.org. It appears to be a very extensive dictionary of hip-hop slang. There is quite a bit of adult material there, as one might expect, so surf at your own risk.