Here's a reference from "The Greatest Spiritual Secret of the Century", by Thom Hartmann, pages 161, 162, 163 and 164. It probably refers to Judas Khrestus, not Rabbi Jesu.
Joshua raised his left hand. "Two thousand years ago, before toilet paper was invented, people used their left hands to clean themselves. They'd then dip their fingers into a bowl of water to clean them, but their left hands were never really clean and they knew it. You know that?"
"I never thought about it", Paul said, dizzied by the sudden change of topic.
"It's true", Joshua said, putting his hand back on the arm of his chair. "In fact, it's still that way in most of the Third World. Today, this is how about four billion people live, without toilet paper. And in those lands today, as back then in Israel, the most terrible and vicious way you could insult a person would be to touch him with your left hand. Even gesturing with the left hand was banned in most societies. Among the Jewish Essenes, gesturing with the left hand would earn you a week's banishment from the community. And if you wanted to really insult somebody, to totally humiliate him, particularly in public, you would slap him with your left hand. You understand?"
"Yes", Paul said. "Like giving somebody the [certain hand gesture] today."
"More like giving them the finger and spitting in their face", Joshua said. "Or throwing [word removed by Swandancer so as not to appear offensive] on them. Remember where that hand was. You'd only do that to a person you knew couldn't retaliate, right? Unless you wanted your [word removed again] kicked."
"Right. So slapping somebody with your left hand, in ancient Roman society, was both the ultimate insult,and also something that was only done to the most powerless people. The Jews whose land was occupied by the Romans, for example. There was no recourse for them, unless it was to punch that person, which would mean they'd get the death penalty for hitting a Roman citizen. You understand?" "Yes", Paul said.
"Unless they could get that Roman to hit them with his right hand, which meant that a fight was engaged. Then they'd be justified to fight back. But the Romans didn't hit slaves with their right hands, they insulted them by slapping them with their left hands and then laughed at the humiliated slave who couldn't slap back."
"Got it."
"So", Joshua said, "which cheek would I strike you on if I wanted to humiliate you by slapping your face with my unclean left hand?"
Paul looked at Joshua's left hand, and then visualised it moving through the air, imagining where Joshua's left palm would fall. "You'd hit my right cheek if you swung your left hand."
"The ultimate vicious and humiliating insult, hitting your right cheek with my left hand."
"Yes."
"And if you then challenged me to hit you with my right hand, that would be a challenge to my authority if I was a slave holder or a powerful person in your society, right?"
"Absolutely. You'd be saying, 'If you have any courage, you'll start a legal fight with me where I can fight back. You'll hit me with your right hand. I dare you. And yet it would not be hitting back, it would be merely exposing the evil of the left-handed slap for what it was."
"I understand", Paul said.
Joshua said, "Ye have heard that it hath been said, An eye for an eye, a tooth for a tooth: But I say unto you, That resist not evil with evil: but whosoever shall smite the on thy right cheek, turn and offer him the other also."