How does Shakespeare show the importance of pride and honor to Benvolio and Mercutio in Romeo and Juliet?

As his name suggests, Benvolio is even-tempered and good-natured. His pride and honor revolves around attempting to keep the peace and being honest. In Act I, Scene 1, he does his best to stop the fight between the Montague and Capulet servants. When Tybalt comes on the scene he urges the Capulet to help him:

I do but keep the peace. Put up thy sword,
Or manage it to part these men with me.

Again in Act III, he tries to keep peace as he pleads with Mercutio to get off the street before the Capulets show up:

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.

He is also the voice of honesty amidst the chaos generated by the street fights in Act I, Scene 1 and Act III, Scene 1. He is forthcoming in his analysis of the brawl in Act I when he explains it to Lord and Lady Montague. In Act III, he describes the fighting to the Prince in honest detail. For all his goodness and honesty, however, Benvolio is helpless to change the course of the tragedy.

Mercutio is prideful and arrogant. He verges on narcissism, especially during his Queen Mab speech in Act I, Scene 4, and in his rant about Benvolio being a fighter in Act III, Scene 1. His pride and honor involves reacting aggressively when he is challenged or perceives some insult.

The best example of his impetuous nature comes in Act III, Scene 1 when he is deaf to the words of Benvolio, who warns him that if they meet the Capulets they will not avoid a fight. Instead of listening, he sarcastically accuses Benvolio of being the fighter. When Tybalt shows up he is increasingly belligerent, attempting to goad Tybalt into a fight. When Tybalt accuses him of "consorting" or associating with Romeo, he says,

Here’s my fiddlestick; here’s
that shall make you dance. Zounds, consort!

Then, when Romeo backs down to Tybalt, Mercutio cannot take it. His pride and twisted sense of honor will not even allow him to accept a friend's acquiescence. He challenges Tybalt himself:

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

His quick temper costs him his life as he is stabbed under Romeo's arm while sword-fighting with Tybalt. Even in death he clings stubbornly to his pride, cursing the families and even joking at his own death:

No, ’tis not so deep as a well, nor so wide as
a church door, but ’tis enough. ’Twill serve. Ask for
me tomorrow, and you shall find me a grave man. I
am peppered, I warrant, for this world. A plague o’
both your houses!