In Act III, Scene 1, what does Shylock mean when he says, "The villainy you teach me, I will execute — and it shall go hard but I will better the instruction" to conclude his speech?
At the end of his Act III, Scene 1 speech in which he argues a Jew feels things just as a Christian does, Shylock tells Salarino he will treat the Christians by the example set for him. In fact, Shylock says he may even outdo the "Christian example" he has been taught.
Shylock, in anticipation of the execution of his revenge against Antonio, hopes to "better the example" of what he calls Christian retaliation. For, earlier in his speech to Salarino, he has said sarcastically,
If a Jew offends a Christian, what’s the Christian’s kind and gentle reaction? Revenge.
Therefore, if Antonio's merchant ships are truly lost, Shylock fully intends to outdo the Christians' examples of revenge. He will demand the pound of flesh from Antonio, who has lost him many ducats in interest that Shylock could have acquired from loaning money if Antonio had not intervened repeatedly. Since Antonio lends money without charging interest as "a Christian courtesy," those in need approach him for loans instead of going to Shylock.