Quite what caplet says to tybalt in anger at the party. Why is he do mad at tybalt?

I'm thinking you mean quote here,

He shall be endured.

What, goodman boy! I say, he shall. Go to.

Am I the master here, or you? Go to.

You’ll not endure him! God shall mend my soul,

You’ll make a mutiny among my guests.

You will set cock-a-hoop. You’ll be the man!

Capulet is all cranky because Tybalt is going to ruin his party. Tybalt is all hot and bothered about catching Romeo at the party but Capulet is fine with it and doesn't want a scene.

Tybalt informs Lord Capulet that a Montague has crashed his party. Unwilling to have trouble at his party, Lord Capulet lets it go............. but Tybalt is annoyed by his failure to react.