The beginning of the novel is similar in tone to
Don Quixote. In other words, it is comical on a level that approaches parody. D’Artagnan acts like a madman and tries to fight the first man who shows him any disrespect. The stranger’s mockery suggests that he is likely a soldier himself who probably has much more experience than d’Artagnan. As such, d’Artagnan’s challenge is ill-advised, especially considering he is alone.