Reasons not to kill a stranger

In traditional New Guinea society, if a New Guinean happened to encounter an unfamiliar New Guinean while both were away from their respective villages, the two engaged in a long discussion of their relatives, in an attempt to establish some relationship and hence some reason why the two should not attempt to kill each other.

(Jared Diamond: Guns, Germs, and Steel)

Not unlike those Greek and Trojan warriors from the Iliad who, when they met in the field of battle, embarked on a prolix enumeration of their respective ancestors before coming to blows. Diomedes and Glaucus not only refused to fight each other, but even exchanged armors.

Also reminiscent of Oedipus, who met Laius at a crossroads and killed him for pretty flimsy reasons.