How is Mr. Antolini's advice ironic?

During their late-night conversation, Mr. Antolini offers Holden Caulfield some advice that is ironic in view of the fact that the inebriated teacher is not following any of it himself. Quoting Wilhelm Stekel, he says, "The mark of the immature man is that he wants to die nobly for a cause, while the mark of the mature man is that he wants to live humbly for one." Mr. Antolini has given up on life. His form of living humbly for a cause is staying drunk on whiskey highballs and being married to an older woman who has a lot of money and is keeping him as a companion and escort. He stays up late because he does not want to get in bed with her while she is still awake. He may have recently lost his teaching job at Elkton Hills, a boys' prep school, because he was showing the same interest in boys that he shows in Holden. He is currently teaching English at NYU. He could not go from a boarding school to an important post at a big university; he is most likely a part-time instructor in an introductory English class and may only teach one course per semester. His advice is not really worth taking seriously since he is not even trying to follow any of it himself. It is the advice of a man who has sold out for security and comfort. He is a "kept man" of an older woman who is "lousy with dough." He is more useful to Holden as a bad example than as a mentor.