Simon's death (Situational Irony)
The plot involves a group of kids in detention in high school, but when Simon turns up dead and the police come ready to deliver murder charges against the innocent children, there is situational irony: he was not murdered. Also, the plot involves a single twist. Unbeknownst to them, the murder was really a suicide, and an angry, hateful one at that. Simon not only killed himself, but he designed the entire event, framing those kids on purpose.
Car accident (Situational Irony)
The car accident is a moment of situational irony because it appears to be a random incident, but as the narrative develops, the teens and the readers discover that Simon had planned it. He paid the driver to crash as a distraction.
Jake's involvement (Situational Irony)
Jake appears to be Cooper's friend and Addy's loving boyfriend, so it is situational irony when he is revealed to be plotting against them. As a friend, he is not expected to adopt Simon's point of view, but because they are both emotionally volatile, they stoke each other to drastic emotional states by encouraging their own feelings of victimhood. The ultimate consequence of that festering is the degeneration of Jake's character until the point he would also betray his own, but he goes even further. Simon wants to pin his death on innocent victims, but Jake literally tries to murder his own girlfriend.
The teens' collaboration (Situational Irony)
What we have in this plot is a kind of "Tower of Babel" story, but instead of nations with their own languages, we have high school kids with their own limited points of view. No one among them knows enough to emerge from the murder investigation on their own, and the title intimates that they will turn against each other. Simon clearly expected this, too. However, expectations are defied when they trust and collaborate, even when the last thing they want is to become vulnerable.
