Why is Mercutio most responsible for the fight in Act III, Scene 1?

In earlier scenes, Mercutio establishes himself as flamboyant, boastful, and edgy. His Queen Mab speech and his treatment of the Nurse prove he's unpredictable. It could also be argued that Mercutio is most responsible for the fight which breaks out in Act III, Scene 1. First, he should have listened to Benvolio. Ever the peacemaker, and well aware of Mercutio's temperament, Benvolio warns him to get off the street. Benvolio says,

I pray thee, good...

In earlier scenes, Mercutio establishes himself as flamboyant, boastful, and edgy. His Queen Mab speech and his treatment of the Nurse prove he's unpredictable. It could also be argued that Mercutio is most responsible for the fight which breaks out in Act III, Scene 1. First, he should have listened to Benvolio. Ever the peacemaker, and well aware of Mercutio's temperament, Benvolio warns him to get off the street. Benvolio says,

I pray thee, good Mercutio, let’s retire.
The day is hot, the Capels are abroad,
And if we meet we shall not ’scape a brawl,
For now, these hot days, is the mad blood stirring.

Instead of heeding Benvolio's warning, Mercutio launches into a sarcastic litany of ways Benvolio is actually the fighter. He names reasons for Benvolio's illusory belligerence:

Thou wilt quarrel with a man for cracking
nuts, having no other reason but because thou
hast hazel eyes.

When Tybalt arrives, Mercutio continues the hard-edged humor by playing on the double meaning of the word consort (either being in league with or a group of musicians). He tells Tybalt,

Consort? What, dost thou make us minstrels?
An thou make minstrels of us, look to hear
nothing but discords. Here’s my fiddlestick; here’s
that shall make you dance. Zounds, consort!

Here, Mercutio is displaying his willingness to fight before Romeo even shows up. He refers to his sword as a fiddlestick in line with his reference to musicians. When Benvolio again urges restraint, Mercutio is deaf. Even though the Prince has forbidden fighting in the street, Mercutio is arrogant enough to ignore that the people of Verona are witnessing the scene. He says,

Men’s eyes were made to look, and let them gaze.
I will not budge for no man’s pleasure, I.

When Romeo enters, Tybalt withdraws from Mercutio and challenges Romeo. Tybalt feels he has been insulted by Romeo's attendance at Capulet's party the night before and wants satisfaction. He says,

Romeo, the love I bear thee can afford
No better term than this: thou art a villain.

Romeo has just married Juliet, Tybalt's cousin, so he rightfully backs down and refers to the Capulets with love. Mercutio, partly miffed that he has been ignored and also enraged by Romeo's acquiescence, steps into the mix and draws his sword. It seems like Mercutio refuses to walk away until there is a fight. In regards to Romeo's apparent cowardice, Mercutio tells Tybalt:

O calm, dishonorable, vile submission!
Alla stoccato carries it away.
Tybalt, you ratcatcher, will you walk?

The fight symbolizes Mercutio's apparent need to prove his manhood and always be the center of attention. The fight may have never occurred if it hadn't been for Mercutio's pride. Shakespeare uses Mercutio's death as a way to move the plot forward and focus the play on the tragedy of Romeo and Juliet.