What are some quotes in Romeo and Juliet that prove Tybalt is impulsive in Act 3 scene 1?
When Tybalt first arrives in Act 3, Scene 1, he approaches Romeo's friends to see if he can find out where Romeo is. He angers Mercutio who becomes a little insulting, but as soon as Tybalt sees Romeo, he says, "Well, peace be with you, sir. Here comes my man" (3.1.57). He has no particular desire to fight Mercutio, as Mercutio is not a Montague. He has no quarrel with this man.
However, when Romeo refuses to fight him, Mercutio feels that Romeo is acting dishonorably and jumps up to fight Tybalt himself. And even though Tybalt has no issue with Mercutio, when Mercutio insults him again, this time, he says, "I am for you" and fights him, fatally wounding Mercutio (3.1.84). This, I believe, shows Tybalt's impulsiveness because he did not come to fight Mercutio, and he didn't even feel compelled to do so when Mercutio became rude and insulting the first time. However, now he's in the mood for a fight, and when Mercutio insults him for the second time, he kills him (which would be a crime that carries the punishment of death if he's caught). Thus, Romeo slays Tybalt out of revenge for his killing Mercutio (also impulsive!).