If you are going to level an accusation like 'the majority of Americans think prisoner-on-prisoner rape is a-ok', then the burden of proof is on you.

I won't even say that nobody thinks that way, I just want proof that this is the prevailing mindset.

It's pretty easy to see that if there's not acceptance, there's at least almost complete apathy. There hasn't exactly been many widespread calls for better conditions in our prisons, and in day to day life, I've never heard anyone suggest it.

The topic of prison rape is a joke that people as a whole feel comfortable laughing about in public.

It is undeniably normative.

Joking about things that are in despicable in reality is commonplace. The TV show "Family Guy" features a pedophile as a main character. Do you think this means the audience or producers feel this is normal and acceptable?

He's not presented in a positive or socially acceptable light. He's funny (to some) because he's transgressive.

People laugh at prison rape because those guys are bad so rape is okay.

I would say that the majority don't care, and depending on how you phrase the question, you could get them to swing either way. The problem is that in public discourse, prison rape is seen as a punchline, not a blight.