Why does the green knight laugh at there responses?

The Green Knight laughs at the responses of King Arthur and his knights because he finds their bravado and bravura amusingly naive. Their eagerness to accept his challenge reflects a mix of courage and foolishness, which he perceives as a lack of understanding of the true nature of his test. His laughter serves to highlight the absurdity of their chivalric ideals when confronted with the reality of his supernatural challenge. Ultimately, it underscores the theme of hubris in a world where honor and bravery must be tested against deeper moral questions.