what type if person is mercutio? how do we know?

Mercutio is brash, tough, outspoken and vulnerable. He is very much an exuberant male adolescent. When the nurse comes to tell Romeo of Juliet's intentions, Mercutio teases her. He tells her to get a fan to cover her face....Yes, Mercutio enjoys being the centre of attention. Infact, he craves this attention. This is where you can say that his "silliness" comes from. He is quick with his wit and uses it to antagonize the Caplets’, particularly Tybalt. There is a part of Mercutio that is up for debate many feel that that he has "feelings" for Romeo (ie. Queen Mab speech) but this is another discussion.