In reference to marijuana - non gritty, nice tasting, potent, clean weed. Most dealers nowadays have inferior marijuana. Most weed smokers are on a continuous search for "the cleans".
Shaggy - "Safe, wanna go halves on an 8th?"
Scooby - "I drunno shraggy, this brer got the cleans?"
Shaggy - "It's not as good as Ted's shit, but he's out of town"
Usually refers to men. Especially men who don't pay much attention to their looks, in terms of grooming, hair and clothes.
However when they put some attention to it they look good.
Best example is Shaggy from Scooby-Doo. He always looks frumpy, stained, unshaven, slump, but you always
get the feeling that when he needs to escort Daphne Blake to her gf wedding Shaggy after a shave and a nice getup will look good.
Girl 1: Are you crazy you want me to go out with Jonah Hill, yuck
Girl 2: Sweety, he cleans up good and will make you look great on that red carpet