Summarize Capulet's scolding of Tybalt in Act 1, Scene 5, lines 77-87 of Romeo and Juliet.

Capulet argues that Tybalt will cause trouble among the guests if he fights Romeo.

There is a feud between the Montagues and Capulets that seems to have gone back generations. It is one of those situations where no one really knows what started it, but the families are willing to die and kill each other over it.  When Tybalt sees Romeo, a Montague, at Juliet’s party, he gets very upset. 

Tybalt has a fiery temper, and wants to fight Romeo there and then.  Capulet refuses. He does not want Tybalt to upset his guests at his daughter's party.  Capulet has a temper too, and is not above taking part in the duel, but he doesn’t want to ruin the party.

Content thee, gentle coz, let him alone;
He bears him like a portly gentleman;
And, to say truth, Verona brags of him
To be a virtuous and well-govern'd youth:
I would not for the wealth of all the town
Here in my house do him disparagement … (Act 1, Scene 5)

Tybalt refuses, trying to defy Capulet.  This angers the man.  He is the head of the Capulet household, and he will not stand to have Tybalt defy him.  He tells him he has too much of a temper and is a spoiled and too full of himself.

You are a saucy boy: is't so, indeed?
This trick may chance to scathe you, I know what:
You must contrary me! marry, 'tis time.
Well said, my hearts! You are a princox; go:
Be quiet, or--More light, more light! For shame! (Act 1, Scene 5)

This lecture works, at least for the time being.  Tybalt knows that he can’t fight Romeo at the party, but he bides his time.  When he sees Romeo on the street, he does fight him.  Romeo does not want to fight, because he is in love with Juliet.  Unfortunately, Tybalt will not back down and he ends up killing Mercutio.  Romeo kills Tybalt in revenge and in order to protect himself.  This is what gets Romeo banished, because fighting in the streets is not allowed.