Finally, I'd like to add that Friar Laurence is quite impulsive in several places. In Act II, scene 3, he chides Romeo for loving Rosaline one day, & Juliet the next, saying
Holy Saint Francis! What a change is here!
Is Rosaline, that thou didst love so dear,
So soon forsaken? Young men's love then lies
Not truly in their hearts, but in their eyes.
Yet only 30 lines later he agrees to marry Romeo & Juliet, arguing that this alliance may bring happiness to both families. This is certainly rash, as he has not spoken to Juliet. He only has Romeo's word that she loves him too. He also agrees to do the marriage in secret, which will prove disastrous later. His next impulsive act also concerns Juliet. This comes during Act IV, scene I, in which Paris announces his intention of marrying Juliet. She is distraught, seeing no escape from this fate. The Friar has a plan though: a poison that imitates death.
If, rather than to marry County Paris,
Thou hast the strength of will to slay thyself,
Then is it likely thou wilt undertake
A thing like death to chide away this shame,(75)
That cop’st with death himself to scape from it;
And, if thou dar'st, I'll give thee remedy.
But just 20 lines earlier he told Juliet that nothing could stop her marriage to Paris! I would argue that the Friar is one of the most impulsive characters in the play, whose rash actions affect all those around him.
Lord Capulet also displays some impulsive behavior in the play 'Romeo and Juliet' by William Shakespeare. He is no spring chicken in terms of age and should know better (through his breeding, maturity and status) than to 'egg on' a fight. Yet, we see him him calling for a sword himself, ready to impulsively throw in his lot and fight with the younger men on his side when he sees a brawl beginning. He also should know better as he has just received yet another stern warning about family fights from the Prince. It seems as if he thinks it's alright to fight outside, as long as it's not damaging his house or property (or perhaps seen by the ladies.) 'What noise is this? Give me my long-sword Ho!' he says. He is concerned at being made a fool of by 'Old Montague.'
I would completely agree with the post above, especially in regards to Tybalt. He is characterized as firey, bloody, and tenacious. He is always ready and willing to fight. Even if you examine some of his dialogue, he used sharp and harsh sounding words. For example, “Peace, peace I hate the word.” Not only in the message aggressive and revealing his impulsiveness, it is a quick like with powerful consonance perforating the beginning of the line. The word “peace
disrupts the sentence, as the rest of the line, “I hate the word,” flows. It is two different mouth movements, where the beginning is slower, and the later is quick and brash.
If you are familiar with the humors Shakespeare used, Tybalt is a prime example of yellow bile. Someone who is easily angered and hot headed. They are also sometimes referred to as "choleric" characters.
Lots of characters show impulsiveness.
Right at the beginning, the servants are impulsive to go and fight in the street just for the heck of it. They are just walking down the street, see the Capulet servants, and start a fight.
Tybalt is pretty impulsive too. He wants to fight Romeo the first time he sees him. And then when they meet on the street after the ball, he starts the fight that ends with him and Mercutio dead.
In the same way, Mercutio is impulsive. He's walking down the street joking like he usually does. Then he sees Tybalt, they insult each other a bit and pretty soon they're both dead.
You could say Lord Capulet is impulsive, saying all kinds of nasty stuff to his daughter just because she asks him not to make her marry Paris -- he doesn't try to explain or reason, just flies off the handle.