Irony of the Red Convertible
The red convertible serves as a symbol of youthful innocence throughout the story, from the time Lyman and Henry buy it at the beginning to Lyman's vandalism when Henry returns home. The car has pleasant memories attached to it, but when Henry drives it to his death, and Lyman sends it into the river after him, it suddenly becomes a symbol of unpleasant loss. Lyman ties it irreparably to death, which is ironic considering its primary symbolism.
Irony of the Picture
The picture Bonita takes of Henry and Lyman before they take their last ride is supposed to be a reminder of their reunion and the joyful restoration of the car. A few months after Lyman returns from the fateful trip, however, he only sees the picture as a representation of terrible memories and Henry's PTSD. It also makes him feel somewhat guilty for Henry's demise, so he takes the picture off the wall and puts it in a closet.
Irony of Native American Medicine
Lyman's mother won't take Henry to a regular hospital, because she's afraid they will pump him full of drugs and keep him. She would rather take him to an "Indian" doctor, but there aren't any she can trust (the only one who might be able to help was jealous of her husbands). The situational irony is that, despite two possible options to help Henry, he can't use either one.
Irony of the Car's Condition
While Henry is away at the war, Lyman keeps the red convertible in great condition, trying to preserve it for Henry for when he returns. The car, symbolizing freedom and innocence, is intended to be restored to Henry, representing Lyman's hope that Henry will be the same as when he left. Lyman's actions in keeping up the car, however, actually represent his own stubbornness in holding on to his youthful worldview.
Irony of Roughhousing
When Lyman and Henry fight, they are using all of their strength, not pulling any punches. Instead of creating a division between them, however, it actually brings them back together again for a moment, the comical situation and shared exertion creating a temporary sense of solidarity and a return to their play-fights of youth.
