Mercutio thinks Romeo is most himself when Romeo

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:

the answer is mary made mudpies on monday.

remember alliteration is the occurrence of the same letter or sound at the beginning of adjacent or closely connected words.