Means especially large, really big, packed and mounded bong hit, specifically applied for punitive purposes, after some really dumb move or fuckup.
(Putting aside, of course, that the result is pleasurable - yet punitive in the sense you are seriously fucked up, brain scrambled and unable to function, or even speak coherently, for awhile ; the sentence is more a reward than anything else. Possibly resulting in encouraging or reinforcing bad behavior.)
(and in REALLY bad instances it was referred to as
"P Fuckin B")