Why did Okonkwo insult a man by calling him a woman at the kindred meeting?

There are several reasons for this.

1. Okonkwo wishes to display his masculinity, and shows it by pointing out that he has titles.
2. Okonkwo wishes to display his masculinity, and shows it by claiming superiority over another individual.
3. Okonkwo wishes to shame the other man into silence and does so quickly and effectively.
4. Okonkwo has no patience for weaker men.