Why does Tybalt seek revenge on Romeo for crashing the party?

Tybalt recognizes Romeo's voice at the Capulet's masked ball, and Tybalt is infuriated that Romeo, a hated Montague, would sneak into the event hiding behind a mask. Tybalt considers it an outrageous violation of Capulet territory, and he believes that Romeo has come to the ball simply to make fun of the Capulets and cause trouble.

TYBALT: This, by his voice, should be a Montague.
. . . What, dares the slave
Come hither, cover'd with an antic face,
To fleer and scorn at our solemnity?
Now, by the stock and honour of my kin,
To strike him dead I hold it not a sin.
[1.5.56–61]
. . . Uncle, this is a Montague, our foe;
A villain, that is hither come in spite
To scorn at our solemnity this night.
[1.5.63-65]

Tybalt's uncle, Lord Capulet, tells Tybalt that he doesn't want Tybalt to cause any disturbance at his party, to "let him alone" [1.5.68] and "take no note of him" [1.5.74]. Tybalt argues with his uncle but eventually abides by his wishes. Nevertheless, Tybalt intends to hold a grudge and to get revenge on Romeo for intruding into the party.

TYBALT: I will withdraw; but this intrusion shall,
Now seeming sweet, convert to bitt'rest gall.
[1.5.96–97]

There's no indication in the play that Tybalt heard what Romeo actually said, only that Tybalt recognized Romeo's voice. Fortunately for all involved, Tybalt stormed out of the party—he might have been even more incensed if he had heard Romeo's remarks about Tybalt's cousin, Juliet, and if he had seen Romeo holding hands with her and kissing her.