Nothing he could do at that age would warrant such a response. Maybe if he stabbed another kid in the eye on purpose.
"... such a response"? I think you're still falling into the trap of evaluating the harshness of the punishment by how heartily the child protests. Have you ever taken a cold shower? Sure, they're not the most comfortable things in the world, but it's hardly less comfortable than a switch, a belt, or a wooden spoon. (And don't give me the old argument about how this is a false dichotomy. The FACT is that my generation - and every other generation before it - was raised this way, that it was not considered abuse by the people dishing it out or by we poor recipients, and that so widely was it accepted that even TEACHERS were authorized to discipline in this manner... they still are in some states. Discipline is SUPPOSED to be uncomfortable, and just because our society has recently decided that causing any physical discomfort in our kids is somehow tantamount to battering a child, doesn't make it so.)
See, I think what's going on is that people hear that child cry and their natural (and proper) instinct is to want to stop the child's suffering. Some people are even suggesting we "kill the bitch." But that mom did not batter that child. She did not initiate the discipline in a blind rage or out of "hurt ego." She did so in response to the child's violation of well-established guidelines and in compliance with well-established methods of punishment. While she does arguably get a little carried away while he's in the shower, at no point is the child's immediate well-being in any jeopardy whatsoever.
So let me ask you this, spidergoat: you've tacitly admitted that a swat is sometimes warranted with little children. What are the parameters or the guideline that YOU would give to parents regarding when it is acceptable to use any form of corporal punishment on a child (age ranges, degree of offense, degree of force used, etc.) Since everybody here wants to second guess this mom... how would you do better?