When Tybalt sees Romeo and says, “Here comes my man,” he means the man that he’s looking for is arriving. Mercutio intentionally misinterprets Tybalt’s phrase “my man,” which could refer to one of a nobleman’s personal servants who wear a uniform (“livery”) that indicates the noble house the servant serves. “My man” may also refer to a follower, a gentleman of lower social rank who owes allegiance to the nobleman. Mercutio jokes that the only sense in which Romeo would be a “follower” of Tybalt would be if Romeo followed Tybalt onto the dueling field where they would fight it out “man” to “man.”