Cesar Milan is a dog trainer. His TV show is “The dog whisperer”. His approach is to treat the master rather than the dog.
The dog only react to his environment. Part of that environment is the body language, mental state and general attitude of their master.
If the master doesn’t have what it takes to give powerful orders to the dog, they won’t listen.
What makes a dog disregard what you tell him ? Lack of confidence, poor body language, no clear vision of what you want, failure to follow through and “make it happen”.
Every dog need rules, boundaries and limitations. Only when they don’t have that they start going wild.
According to Cesar, the Chihuahua is the most antisocial, aggressive and bad behaved breed. Why ? Because it’s so cute nobody ever find it necessary to discipline them. They are covered with love, affection and gifts. That’s why they believe they are in charge the center of universe, thus the crazy behavior.
Big dogs on the other hand are generally very well behaved, especially the pit bull. Why ? Because they are scary and the slightest barks is corrected right away. We can’t allow them to escalate. They have strong rules, boundaries and limitations. That makes them balanced and very nice dogs.

It works the same with humans. If you raise your children like they are kings and queens. If you never disagree with their poor behavior. If you can’t follow through with your demands. If you can’t make yourself respected. If you shower them with presents. If you never make them face their responsibilities because you’re mistaking being firm with being mean. If you can’t show them a proper attitude because you mistake being nice with being weak. Then of course they’ll end up believing the world owe them and actually be assholes.
It’s not a gender issue. It just happens to be way worse for women for the exact same reason Chihuahuas are worse than dangerous breeds. Nobody ever disagree or discipline women because we mistake being firm with being mean, and just like Chihuahua they are so cute.

The best tool Cesar has to help dogs get out of their emotional/mental spin is to firmly touch them in the neck with two finger. The intention is not to hurt them, he just wants to startle them so they can refocus their mind on something else and forget about what they were doing the second before.
It works the same with humans. That’s were the slap is misunderstood greatly.
Slapping a woman (or a child), when done appropriately is not meant to hurt. It’s just meant to help the woman to break free of their mental whirlwind. That’s why it’s a very technical move. You can’t slap anyone when you’re angry yourself. Because you’ll convey the wrong message, you’ll overdo it and probably put too much strengh. In that scenario you’re rightfully so the bad guy.
Since slapping has such bad press, I recommend any other gesture that accomplish the same purpose. A firm touch that forces the person to refocus on something else. My personal favorite is to grab the shoulder gently squeezing, look directly in the eyes and calmly call the person by their name until they shut up/calm down.
The timing is very important because if you wait too long, they won’t be able to come back from the mental turmoil. That’s why it’s very important to never let things escalate. The very second you see the person going from angry level 0 to level 1 it’s time to touch and get the discussion back to Earth. If you wait for level 2 or more, it’s too late.

TL,DR : your mental state and personal energy greatly influence people around you. In fact people’s attitude towards you is the direct mirror of your own inner reality.
You can (you should ?) prevent people from escalating their emotions by touching them (or doing anything surprising). Because once they get the hamster spinning in real time you can’t stop it.

EDIT : "That’s were the slap is misunderstood greatly". In other words it means reconsider what you think about the "slap" because it's mostly wrong.
Just to be absolutely clear. It doesn't matter what you do (touch, slap, snap your finger, etc) it's all about how you do it AND your mental state at the instant you do it. By the way it's exactly why the same pick up line (or behavior) will either be felt as creepy or charming. Words don't matter, it's who you are at the moment you deliver them that matters.