Smiling in these scenarios is for people who are really, really comfortable with their sexuality and/or themselves. You would be holding yourself to a high standard of comfort and self-harmony to demand a smile from yourself, and forcing it would be wrong for a number of reasons, which I'm sure you already are aware.
I can talk about more philosophy and history than anyone would care to know, and go into great depth on a lot of intellectual subjects - but at some point I realized that things like smiling, dancing in a carefree way, being open and easy with people, just enjoying the simple sensations of myself and my body - I realized that these would be lifelong paths for me to walk and challenges for me to enjoy. I will never be at the level of a vivacious, easily flirtatious guy - I am too heavily loaded with intellectual/emotional/spiritual stuff for that groove to come easily. But we can all make moves in whatever directions we choose.
Those of us who are not carefree, dancing, basic-life-enthused types, will always have to study and respect those who are, and try to learn ways to approach that kind of groovy way to be. Likewise those who are carefree, if they want to learn about the stuff we know about, will find it a difficult and lifelong path for them to approach wisdom and self-containedness. [EDIT: You may not think of yourself as wise and self-contained, but compared to most people, you probably are.] I'm assuming that all reading this will tend to be more analytical/neurotic/self-contained types, thats why we choose an intellectual medium to help discover our sexuality.
A lot of our pain comes from trying to imitate or hold ourselves to the standard of, people who are fundamentally different in their development trajectories. An analytical guy becoming "High School cool" doesn't really make sense. Its like those mythological creatures with the head of one animal and the body of another; those creatures don't exist in the wild, and some of our 'alpha' concepts don't exist outside of Pickup boards. But I digress.