In this excerpt from "Romeo and Juliet", Act III, Scene I, Shakespeare includes this comic speech by Mercutio to mock the reasons for quarrels and feuds.
Mercutio tells Benvolio that he cannot be his tutor to prevent him from fighting because he is always fighting. And Benvolio answers him back. Mercutio is the clever character who makes puns and jokes on the other characters. He doesn't believe in fate and knows clearly that the violence between the Capulets and the Montagues is the cause of all fights among the members of the two families. This excerpt is foreshadowing Mercutio's death and the way in which he dies cursing the hatred between the two families.