The ironic soldier romance
An already ironic story becomes more ironic when a young girl decides to ask a man out, a veteran soldier from WWII, no less. Amazingly, he accepts, and then something terrible happens when he tries to take advantage of her sexually. All this serves to indicate that Frankie is indeed not an adult, with a rude awakening to boot.
The ironic name change
When she has an identity crisis, instead of fixing herself to what she knows, Frankie's curious, rambunctious nature leads her to reject the identity she knows for herself. She does this in the name of maturity, but it's actually a sign of her immaturity, because she tries to change her name. This doesn't change anything about her, except her persona, but it does illustrate that she's eager to move into her puberty, so ultimately her eagerness is a good thing.
John Henry's death
The ultimate irony for any young person is death. When inevitably, someone dies, it can often come as a surprise. Although "F. Jasmine" already knows death indirectly since her uncle dies, she doesn't really have to face that in reality until it's her little baby cousin, her very own bedmate. His death is terribly ironic, but death itself is absolutely not ironic for Frankie. She must learn that lesson without games or fun.
The ironic stowaway
If Frankie had gotten what she wanted, there would have been a stowaway when Jarvis and Janice left for their honeymoon—ironic no doubt. But the attempt itself is unexpected. Why would a young person in an identity crisis want to go on her brother's honeymoon? It's because she is envious of his real adult life, and she is curious to know what there is for her in the world by way of sexuality. We know this because she also approaches an adult in a more-or-less romantic way (not that she knows what she's doing).
The irony of racism
When the black maid finds herself talking with Frankie about gender inequality and the differences between certain kinds of people, suddenly they have an interesting moment when they discover that they have quite accidentally backed up into the topic of racism. They share a puzzled moment and acknowledge how truly abominable and sad racism really is. Not to mention that it's completely unfounded and unnecessary.