Answer:
When Romeo refuses to fight in Act III, scene i, Mercutio thinks that Romeo is being a coward. Tybalt had earlier sent a "challenge" to Romeo's house, and Mercutio expects Romeo and answer it. When Tybalt goes further in this scene and calls Romeo a "villain" (III.i.64), Mercutio expects Romeo to stand up for his own honor and defend himself.
Explanation:
