When Tybalt sees Romeo at Lord Capulet's masquerade party, he becomes instantly enraged, feeling as though the young Montague's presence is an insult to his family's honor. He wants to confront Romeo himself, and is rushing off to do so when Capulet stops him. Tybalt explains that he's spotted Romeo and details his belief that the young man has come "in spite" to mock their festivities (1.5.70). However, Capulet, quite reasonably at first, instructs Tybalt to leave Romeo alone and not to let his presence be a bother because Capulet would never treat Romeo badly in his own house, especially not in front of his guests. He says,
Take no note of him.
It is my will, the which if thou respect,
Show a fair presence and put off these frowns,
An ill-beseeming semblance for a feast. (1.5.80-83).
In these lines, then, Capulet seems to demand his nephew's respect for his will, asking him to stop being upset and just enjoy the party. However, when Tybalt says that he cannot endure Romeo's presence, Capulet becomes angry, saying,
He shall be endured.
What, goodman boy? I say he shall. Go to.
Am I the master here or you? Go to.
You will set cock-a-hoop, you'll be the man! (1.5.86-91)
Here, Capulet insults Tybalt, calling him "goodman boy," emphasizing Capulet's rank as a gentleman above Tybalt, and then he further underscores the disparity between their respective statuses when he rhetorically asks who the master is here. (It is obviously Capulet.) Finally, he accuses Tybalt of recklessness when he says that his nephew "will set cock-a-hoop," and mocks him for wanting to "be the man," and, essentially, take charge (over Capulet, his uncle). Thus, Capulet says quite a few things to reinforce his power over Tybalt: this is his home, his party, his guests, he is a gentleman, the master, the man in charge.