I read this, I think, in an unremembered anthology about 25 years ago but the style/language made me think of the early 1960s.
The tale begins with a mid-teens protagonist deciding if he can be bothered raping anybody today. The backstory is then revealed, we are in a post-nuclear war community set amongst a vast system of bunkers, caves and tunnels, with open bush country between them all.
The boys all seem to get raped often throughout their childhood until they're big enough to fight back - the girls just endure. When the boys get bigger, they themselves then begin to prey in the same way on the younger kids.
The current ruler of this area is 'Buddy', a fearsome bully. He spends most days glowering at anyone who goes near the cooking pots. These are tended by older men and women (commonly known as 'creeps') who live under Buddy's rule for a peaceful life. The pots are constantly stocked with grain and root vegetables farmed by other 'creeps' - and some 'creep' hunters who trap possums and squirrels etc.
Buddy is known for suddenly killing a person and throwing them to the 'creeps' to stock the stewpots up. No meat gets wasted in this harsh life. The boy witnessed him one day when a 3 year old girl innocently walked right up to the cooking pots to speak to a stirring woman, he picked the child up and plunged her alive into the bubbling mix, there was extra meat for all that day but the brutal lesson lingered.
Anyways, the teen boy decides he'll go see the 'funny guy' again and he sneaks away down long deserted tunnels until he reaches a big rock fall. He first found this place as a young kid hiding from a rape gang. He slithers through tight places and emerges in a pitch-black room, feeling about he finds an ancient light switch and reveals a battered computer console with a human head mounted on it. He gives it a "Like, start talking, man".
A second backstory reveals the head is of a scientist, he and his team were in a nuke bunker in the caves, waiting for www3 to commence, and came up with an idea to hand knowledge down to the survivors. They drew lots (I think) to select him, then set his head up in the console and loaded it with life preservation stuff.
However the blast brought down the rockfall and left him there alone for countless decades until the boy found him. The boy has visited several times but finds his donnish way of speaking very boring. Also the scientist is appalled at the beatnik speech of the boy.
He has to tell the boy, yet again, what bombs are, but again he realises all the boy wants is a way to get a bomb, kill Buddy, and seize power.
He tries a bit of Bible preaching but the boy says "that's s**t man" and goes to leave, saying over his shoulder that he probably won't ever be back because he's getting too big for the crawling space.
I think it ends with the head desperately pleading for the light to be left on, he doesn't want to spend millenia in the dark. No use; the teen casually flicks off the light and crawls away through the gaps
Update in March 23: I've had this same question posted on other sites but no luck with an answer, I can't remember anything else so I'm going to post a bounty - hopefully there's a newbie since I asked who might recognise it
