S of B
Explanation
The Joke
A man angrily calls someone "You son of a bitch!" The other person corrects him: "That's incorrect. My mom died years ago. There are several of us." The first man adjusts: "Better, but we all have a mother in common." The corrected person then retorts: "Just said I'm the only one. Coming to you, grammar-wise, 'son of a bitch' implies you are insulting my mother, and at me. Additionally our parents were married, so 'bitch' doesn't apply either." The first man tries variations: "You... son of... you..." then "You son of bitches!" and finally settles on "You son of bitches!" to which the other man responds "Very good!"
The comic takes the common insult "son of a bitch" and subjects it to rigorous logical and grammatical analysis. Each correction forces the insulter to refine his language to make the insult technically accurate -- accounting for the mother's death (making it past tense), the number of siblings (making it plural), and the marital status of the parents. The final formulation "you son of bitches" apparently satisfies all the pedantic objections.
The Humor
The humor comes from the absurd clash between the raw emotion of hurling an insult and the calm, pedantic deconstruction of its grammatical and factual accuracy. It is funny because insults are not meant to be literally accurate, yet this person insists on treating the phrase as a factual claim that must be corrected. The escalating frustration of the insulter as he tries to satisfy increasingly specific objections, combined with the satisfaction of the pedant when the "correct" version is finally achieved, creates a comedic dynamic familiar to anyone who has dealt with an insufferable stickler for precision.