Can you please close the door after me?

Last night we were planning a farewell dinner for a friend and he didn't show up. In retrospect, I realized he had to leave the next day and he had too many things to finish which blurred his memory, but during dinner, I was pretty pissed. Anyways, we made really good food and the episode of The Big Bang Theory we watched while eating helped a lot in lifting the general mood of everyone. At end of it, my stomach was very full and I was debating whether I should sleep or read something for my term paper. I was lying in bed and the temptation to sleep was slowly winning when somebody knocked my bed room door. It was my room-mate and he was standing right outside when I opened. He said, "I am going to lab", to which I replied "OK". He then continued, "Can you lock the main door after I am gone?". Let's pause here for a moment and try to assimilate the situation. He had a key with him. In fact, our door doesn't even need a key to lock! It is one of those doors on which you turn some knob before closing to lock it. Also remember that I was about to sleep and he dragged me out of bed. I stared at him for a moment, trying to figure out what he really wanted from me. Was he trying to say that if I closed the door myself, I would be safer inside? This by extension would mean that he doesn't know how to lock the door, which if extended further makes me wonder why nobody has robbed our apartment already during the last two years we've been staying together! Since everything is safely scattered inside the apartment as they should, I assume he does know how to lock the door. Then what else could it be? Did he think that, in the interest of the whole universe, it would be more energy efficient if I closed the door? Was it more efficient to stand outside a sleeping man's bed room, wake him up and then force him to lock the door than to just pull out his key and lock it? It perplexed me so completely that words failed me. To be honest, even though I was thoroughly irritated, I had to fight a sudden impulse to laugh out loud. In the end, the best repose I had to his request was a middle finger!! He took offense to that and left with a look on his face that clearly said "Can't even ask for a simple favor!"