In the very first scene that Shylock and Antonio appear together in The Merchant of Venice, Shylock says that in the past, Antonio has treated him cruelly because Shylock is Jewish. Shylock says Antonio called him a
misbeliever, cut-throat, dog / And spit upon my Jewish gaberdine. (I.iii)
Shylock also says that Antonio kicked him on the street like a stray dog:
[You] foot me as you spurn a stranger curOver your threshold! (I.iii)
I don't know about you, but being called cruel names and being spit at would make me pretty upset!
We know that what Shylock says is true, because Antonio himself confirms it. Rather than denying the name-calling and spitting, he agrees that he's done it many times before and will continue to do so. He is not appealing to Shylock to lend him money as a friend, but as an enemy.
In my dictionary there is an example of how the word "justice" might be used: "He's angry, and with justice." In student guides and elsewhere we find attempts to justify Shylock's anger. His demands, as Salerio reports, are about forfeiture, justice and his bond. It is clear that to allow the forfeiture would be unjust. Therefore, Shakespeare provided linguistic connections to ROMEO AND JULIET throughout the play. One example, Romeo's "The time and my intents are savage-wild, / More fierce and more inexorable far / Than empty tigers or the roaring sea"(ROM5.3) corresponds to the following in MV: "You may as well go stand upon the beach / And bid the main flood bat his usual height; / You may as well use question with the wolf.............inexecrable dog"(MV4.1).