How to respond to a challenge
Walk away.
Why?
1. If the other guy is stronger or a better fighter than you, you are going to get your a** kicked.
2. If you are stronger or a better fighter than the other guy, you might hurt him (kill him?) and end up in prison. And if you don't end up in prison, you might have that infliction of damage on another human on your conscience forever.
I learned a long time ago that "you" should never show up to a fist fight with just your fists, bring a knife or a club... never show up to a knife fight with a knife, come with a gun. Never bring a weapon, unless you are willing to use it (if you don't the other guy is going to take it away and use it on you)... never bring a gun unless you are prepared to drop the hammer (or the other guy is going to take the gun and kill you or someone else). Most to this will end up with you in prison or a hospital or a grave.
War aside, getting into fights is a really bad idea.
When challenged, walk away and let the other guy think that he has won. You lose nothing.
Now, if the other guy attacks you, you must fight to win... to quote a line from a famous movie, "there are no rules in a knife fight." You must end it and end it fast... the longer you fight, the greater your chance of losing (unless you are Muhammad Ali fighting George Foreman in a controlled boxing bout).
Now, if someone physically attacks your mother/wife/daughter/etc.... attack fast without warning, without remorse, without hesitation... do not stop until the person is crushed to the ground beyond movement... if the person has friends, they must also be crushed beyond movement...
If the Mafia comes calling, kill them all... turn on them so hard that they are completely destroyed or you are dead, with the Mafia the game will be on forever... you can never stop, never retreat, never have a truce... your life will be a giver of death... forever. Same goes for terrorists.
The end.