Smiling is the way humans show happiness, and the way most predator animals show that they are mad as hell and are going to kill you if you don't get the hell away from them. Another example of the animal kingdom being way more badass than humans.
Smiling is contagious; it's like polio for your face. Everybody has been in a situation where one person smiles, then another smiles, and then another, until the whole room is composed of nothing but smiling people. Then everybody gets all creeped out and stops smiling, and go back to their conversation about child molestation or something.
More useful is the fact that people have an easier time getting through a difficult time by smiling. If a rich grandparent is dead, and you end up out of the will, just SMILE! That will make everything better, somehow. Maybe if everybody smiled more after 9/11, we'd have gotten over it sooner, and maybe even give Rudy Giuliani a life beyond "the guy who was NYC mayor at the time".
And to make face-AIDS even more of a cheat code in life, when you smile your body releases chemicals that automatically make you happier. Sadly, the chemical isn't sex-related, but it's still pretty cool; essentially it makes you get happier, put others in a good mood, and get in trouble less.
Nah, just kidding. There's nothing badass about smiling. It makes you look like a total pussy. If you're a gang member (for example), and you smile, you'll look like even more of a douchebag then you already are. Seriously, get a job, dicks. You're wasting your life.
Anyway, while humans just look like idiots when they smile, with animals it's a little different. Don't get me wrong, they still look like dicks, but in this case it's a real bad idea to point and laugh at them. If you do that, they will find you and strike you down. Hard.
Okay, we've already discussed what ISN'T cool- smiling. You are never cool while you're smiling. It's a fact that I've already stated, so we'll skip ahead a bit.
So, what DOES make you cool? Frowning! It takes like, a hundred muscles to frown, which as you can see is more than the 33 it takes to smile. Therefore, frowning tells people that you can totally handle the hard stuff, because look at all of those muscles you're using! Kickass!
Plus, as it shows above, smiling is healthy for you, so going by that logic I guess frowning is not. This also makes it awesome to frown, because anybody who frowns clearly doesn't give a shit about themselves, and that is cool to some people. Not me, but some people.
Don't smile. It can make you look stupid and douchey, and sometimes it may even remind people of Pauly Shore. That's a bad thing, and it definitely isn't worth it. And that's all I have to say about that.