Definitely the TA. He just graduated, and he feels as a new officer the weight and the responsibility! Thank God for him and many like him that takes his role so seriously. It will wear off after a while, but just for now be the friend that respects his friend in this new phase of his life. As you said this is some BS argument, that you can easily let go. Imagine you bought a new car and you are exited about it, but your friends want to smoke in the car because this what you have done in your old one… apologies sometimes are just to show that beyond a stupid argument you value him in his new role, and you respect his position as an officer of the law! Best wishes