Well you probably could if you don't care what you look like. If that's the case you may as well pick up a really cheap one at a second hand shop. Nothing wrong with that I guess but isn't the point of wearing one to look nice? Actually I didn't give a shit for prom either, but I did rent a tux this past weekend because I was in a friend's wedding. All you do is find a tux shop nearby, go in and they'll measure you and shit and have you try on shoes. Then like the day before the event you have to go in to pick it up. At that time they'll make sure everything fits. Don't forget to take it back the next day.