Final answer:
The teen was missing the character trait of responsibility in this situation.
Step-by-step explanation:
The good character trait that the teen was missing in this situation is responsibility.
Responsibility refers to the ability to be accountable for one's actions and make wise choices. In this case, the teen showed a lack of responsibility by using his older brother's ID to buy beer and by drinking behind a convenience store.
By engaging in underage drinking and using someone else's ID, the teen demonstrated a lack of responsibility, as he disregarded the laws and the potential consequences of his actions.