
It's a nickname for Tybalt.
Romeo & Juliet, Act II, scene 4
MERCUTIO
Alas poor Romeo! he is already dead; stabbed with a
white wench's black eye; shot through the ear with a
love-song; the very pin of his heart cleft with the
blind bow-boy's butt-shaft: and is he a man to
encounter Tybalt?
BENVOLIO
Why, what is Tybalt?
MERCUTIO
More than prince of cats, I can tell you. O, he is
the courageous captain of compliments. He fights as
you sing prick-song, keeps time, distance, and
proportion; rests me his minim rest, one, two, and
the third in your bosom: the very butcher of a silk
button, a duellist, a duellist; a gentleman of the
very first house, of the first and second cause:
ah, the immortal passado! the punto reverso! the
hai!