Pinkie accusing Rose of being "green" (Dramatic Irony)
Even though Pinkie is quite young and a virgin just like Rose, he condescends upon her, saying that she is naïve and does not understand love and sex. It is because the two are so similar in this regard that Pinkie is able to feel better about himself by denigrating her; he distances himself from the part of himself that he feels shame for.
Colleoni the clean gangster (Situational Irony)
When Pinkie is brought into the police station for questioning about his assault of Brewer, the investigator explains to him that they prefer Colleoni's breed of gangster: less inclined to violence; more concerned about the preservation of order rather than the accrual of pride. Colleoni, though a criminal, lives a very rich and comfortable existence, and he does not have to take on the threatening pose of the criminal. He has, as he himself claims, become a businessman.
Opposites attract (Situational Irony)
As Pinkie himself realizes, he and Rose are diametrically opposed characters: He is evil, and she is good. Rose also realizes this, but this only makes her agree with Pinkie in their contradictory romance. Rose's goodness is a goodness more closely related to Pinkie's evil than to Ida's goodness.
Pinkie's vitriol (Dramatic Irony)
Although Pinkie keeps his vitriol as a last-resort weapon, especially against Rose, and threatens her with it, it is, in the end, he himself who feels the searing burn of the acid. This represents the way his own poisonous personality, which he had thought made him a tough criminal, destroys him.
