He may not know whether or not he stinks, but by not showering in the morning it's unlikely he doesn't. Others around him may not inform him, as they may be more considerate about his feelings than he is about their sense of smell.
I do this too. I shower before bed and spend 5 minutes in the bathroom shaving, brushing my teeth, styling my hair, and urinating.
My argument is that you need to shower at the end of the day to get all that gunk off of you.. otherwise you're just sleeping in your own dirt!
Sure. Our faces are exposed to the elements all day - worse if you live in a busy city. Showering before bed also keeps the sheets cleaner.
However, 5 minutes is not long enough unless you're very talented, doing most of these simultaneously. Teeth alone take at least 5 minutes (proper brush, tongue, scrape, floss, mouthwash). Someone also mentioned a dump in their 5 minute routine - this is not taking time to properly experience what must be the second or third greatest pleasure we have. Take the time.
8 hours lying around in a warm bed? Probably no less than 8 hours up and about. We're at least airing ourselves when we're up.
I suppose not if you don't have sex, sweat, or have clothes that repel body oils and dead skin cells.