Devin has a little too much of a hero complex. I'll attribute his rashness to his youth and immaturity. The incident in the parking lot turned out well only because the single minded moron wasn't armed. He was certainly stupid enough to have used a weapon if he had one regardless of the consequences. I think Devin's elders need to school him to be more cautious. He should have knocked the guy out instead of toying with him.
The whole business of the house key came off poorly to me. While Mac's reasoning was sound, he gives more of an impression of a whiner.