it can mean cool, or drunk, or uncool, or shitty, or hot, or whatever, based on the connotation.
eg. (drunk) "man, i was so fuckin sliced last night!"
(attractive) "damn that dude is slicin'!"
(disgust/embarassment) "yo girl, that's sliced."
the act of sweating in the underarm area, therefore creating a bologna slice shaped stain on your shirt (grey is the worst color to wear while slicin)
Oh no its hot in here, im slicin like a mofo, grey was a baaad choice.