Ok, first of all, PB has, for over 35 years of personal knowledge, meant PENALTY BONG. And ONLY Penalty Bong. Pre-dates by decades, Pussy Bitch or Penis Breath or even Peanut Butter!
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.)
“Oh wow Dude, you did NOT just…..spill all the rest of our dope on the floor / tell your Dad we just dropped acid (a personal best – fuck, another PB!) / pee yourself / tell that cop we were stoned / smoke all that joint without givin’ me a hit / eat all the rest of the chocolate chip cookies / do your girlfriends Mom and not invite me - PB - penalty bong!”
(and in REALLY bad instances it was referred to as
"P Fuckin B")