I've never found prison rape to be particularly funny, and after editing an article about the shortfalls of the Prison Rape Elimination Act, think that it's the ugliest symptom of an array of problems in the American system: overcrowding, lack of rehabilitation, cut ties with the outside world, etc. That said, I can recognize the irony of deeming a child molester to be too small and easily-victimized to go to prison. Milbarge has pointed out that "there are some cases approving sentencing departures because the defendant is unusually susceptible to prison violence or sexual assault."
Perhaps we need a penal alternative to prison. I'm not sure what that could be, as the 8th Amendment precludes many of the historic options like corporal punishment. Does anyone know if the stocks are considered corporal punishment, or otherwise are forbidden by the 8th? After so many years of disuse, it might fall afoul of the "unusual" provision, but if putting short people in prison is too cruel, we're going to have to get creative. As our standards of cruel and unusual have evolved, prison appears to have devolved into inhumanity, so that confinement with other offenders is tantamount to a sentence to be brutalized.