The irony of pleasure
Holofernes feels entitled to pleasure, which is a sign that he is a bad leader, because he is clearly someone who exploits his authority to get what he wants. He doesn't impress women. He forces them into sex slavery, raping them under the very real threat of death. He is ironically oriented to pleasure, which is also shown through his relationship to alcohol. Even though the pleasure of alcohol literally weakens his ability to be powerful, he feels entitled enough to get drunk anyway. This leads to his assassination.
Judith's ironic weakness
The misogyny of Holofernes is paired with an ironic reminder of Judith's weakness. Quite literally, her weakness only matters once, and it isn't important to the story, except that she has to hack Holofernes's neck twice to decapitate him. The only way her weakness matters is that she can't quite give Holofernes a painless death. Instead, he has to suffer unimaginable pain for a half second while she withdraws the blade and takes another swing. She is weak, but death by her hand is not less gory or painful, but twice as gory and twice as painful.
The irony of Israelite victory
When Judith says the Israelites will win if they invade Assyria, that is ironic, but not as ironic as her trophy—Holofernes's bloody, rotting head. The symbol is that the victory is already attained, and why will they win? Even though they are outnumbered, they will win because the Assyrians are drunk. Judith knows because she was technically out-manned in her battle with Holofernes, except he was drunk. The city is merely a vestige of Holofernes's ended reign.
The irony of Judith's glory
Instead of taking spoils from battle, like the Israelites, the true hero of the story chooses to keep nothing from these stories for herself. Instead of accepting her heroic entitlement to her boon, she chooses to accept glory alone, symbolizing this glory by saying that she will get her recompense in the afterlife, when God judges her as a faithful servant. This is a mythic way of saying that she feels her reward was implicit in her ability to serve her community for God.
The ironic God of violence
For people who are not familiar with the Bible or its stories, the irony of this anonymous poem might be especially striking. Although the author of this story is presumably Christian, accepting Christ as the ultimate symbol for God's identity, the author chooses to illustrate God's action in the world through the goriest, most brutal kind of story. The irony is that when people use their power for evil, God's goodness is mythically depicted in the most vengeful, violent, gory way. Justice is ironically bloody.
