Casting stones

So, the carpenter's son is strolling through downtown with his posse and they come up on a mob harrassing a lady.
He asks them "what's up people. Why are you messing with the dame?"
"She is a bad woman and we can't have people like her living amongst us" they said.
The carpenter's son said to them "Let he who is without sin cast the first stone".
The crowd slowly disperses.
Then one woman picks a stone and throws it at the woman.
The carpenter's son turns to her in exasperation and says "sometimes you really piss me off, Mom!"