His banter suggests long friendship with Romeo and can become far out -- like way out. For example:

Mercutio: No I am the very pink of courtesy.
Romeo: Pink for flower?
Mercutio: Right.

Besides being a flower, he is also a center of attention. Romeo describes him as "a gentleman... that loves to hear himself talk."

If one cares to be superstitious, the ending of Romeo & Juliet can seem affected by Mercutio's curse on both the House of Montague and that of Capulet. As he dies, from Tybalt's blow, he proclaims, "A plague on both your houses!"