In The Merchant of Venice, what is Antonio's response to Shylock's accusation that Antonio has treated him badly?

Shylock's tirade against Antonio is found in Act One, Scene Three. Bassanio has just spoken to Shylock about the loan Antonio had asked him to make, using his good name and status as a trader as a guarantee. When Antonio arrives and asks Shylock whether he will grant the loan, Shylock says the following:

Signior Antonio, many a time and oft
In the Rialto you have rated me
About my moneys and my usances:
Still have I borne it with a patient shrug,
For sufferance is the badge of all our tribe.
You call me misbeliever, cut-throat dog,
And spit upon my Jewish gaberdine,
And all for use of that which is mine own.
Well then, it now appears you need my help:
Go to, then; you come to me, and you say
Shylock, we would have moneys:' you say so;
You, that did void your rheum upon my beard
And foot me as you spurn a stranger cur
Over your threshold: moneys is your suit
What should I say to you? Should I not say
Hath a dog money? is it possible
A cur can lend three thousand ducats?' Or
Shall I bend low and in a bondman's key,
With bated breath and whispering humbleness, Say this;
'Fair sir, you spit on me on Wednesday last;
You spurn'd me such a day; another time
You call'd me dog; and for these courtesies
I'll lend you thus much moneys'?

Shylock here accuses Antonio for treating him with prejudice and contempt. He has often and regularly criticised Shylock about his money and the fact that he lent out capital at interest. Shylock further mentions that Antonio had called him a dog, a heathen and ruthless and that he had spat on his Jewish cloak and all because he used whatever belongs to him (i.e. his own money) so that he may profit. He further accuses Antonio for having spat on his beard and kicked him as he would a bastard dog from his doorway.

It is clear that Shylock is deeply aggrieved at the insulting and humiliating manner in which Antonio had treated him. He asks whether he should not ask rhetorical questions such as, 'Does a dog have money?' or 'Can an unbred hound lend three thousand ducats?' He sarcastically asks whether, in spite of the terrible treatment that Antonio meted out to him, he should, for these kindnesses lend Antonio such an extensive sum of money?

Antonio replies:

I am as like to call thee so again,
To spit on thee again, to spurn thee too.
If thou wilt lend this money, lend it not
As to thy friends; for when did friendship take
A breed for barren metal of his friend?
But lend it rather to thine enemy,
Who, if he break, thou mayst with better face
Exact the penalty.

Antonio is clearly unrepentant and says that he is more than likely to ill-treat Shylock in the same manner. He suggests that Shylock should not lend the money to him as he would to a friend, but as to an enemy. He suggests that friendship would never allow a friend to ask interest once he has lent money to another (unlike Shylock). This would give Shylock a justified reason to punish him if he should fail to meet the terms of their bond.

The two eventually agree that Shylock will lend Antonio the money free of interest with the condition that if he should forfeit in settling the debt within three months, he should give up a pound of his flesh to shylock from whichever part of his body Shylock deems fit.