It's rude to swear at people.
James is riding his bike when he gets cut off by a vehicle driven by Sean.
James wants to express his anger at Sean.
James tells Sean that he almost killed him and tells him to be more careful before he ends someone's life.
James tells Sean that he is a fucking piece of shit who doesn't know how to drive.
Sean feels embarrassed for his mistake, apologizes to James and vows to drive more carefully.
Sean feels the need to reclaim his masculinity and gets out of the car aggressively which leads to a physical confrontation.