Answer:
I would say it would have to be the hormonal saturation of the frontal lobe (the executive function, reasoning, and decision-making part of the brain).
Explanation: At that age a teenager's brain is in the middle of crucial development and is being flooded with hormones especially around the frontal lobe, affecting their reasoning and decision-making skills, which may cause them to be irrational and have a hard time calming down.