Does the law say you have to take it?
But you dont get to kill someone just because they punched you in a bar. Sorry.... that is not how the law works. If someone is punching you in a bar you dont automatically get to pull out a knife and stab them repeatedly. You can use equal force if reasonable or perhaps force to save yourself such as grabbing an item and hitting the person so that you can escape.
Also if you kill someone in a bar fight you will be arrested if you instigated the fight, continued the fight without fleeing when safe to do so, or escalated the encounter. If you are punched silly I doubnt you can defend yourself anyway. But if you get up and go stab the person in the neck and kill him....get ready for a trial.
As for what you never heard of:
Article 35 of the New York Penal Law Code explains when individuals are “justified” to use physical or deadly force to defend themselves or others. New York Penal Law 35.15 states that you can use physical force when and to the extent, you reasonably believe such to be necessary to defend yourself, or another individual from what you believe to be the use or imminent use of unlawful physical force by another individual. However, a person may only use deadly physical force in limited circumstances. For instance, if an individual reasonably believes that another person is committing or trying to commit a kidnapping, forcible criminal sexual act, forcible rape, or robbery, they may use deadly physical force.
New York is governed by the concept of “Duty to retreat” and the “Castle Doctrine.” The duty to retreat concept means that before a person acts in self-defense, they should take reasonable steps to mitigate the risk of harm. Generally, the duty to retreat concept requires that an individual only uses force as a last resort.
Deadly physical force which is the type of force that is capable of causing a serious physical injury or death is not permitted unless a person reasonable believes that deadly physical force is being used or is about to be used on himself, herself or a third person. Even in such a situation however, the law imposes on a person a duty to retreat before he or she can resort to using deadly physical force if they can retreat with complete safety.