Social smile vs Spontaneous smile

I have great difficulty smiling politely but spontaneous laughter at a joke comes easily. This is true even in the situation I described in my last post. I had always wondered about this till I came across a passage in How the Mind Works:

Facial expressions are useful only if they are hard to fake. As a matter of fact, they are hard to fake. People don't really believe that the grinning flight attendant is happy to see them. That is because a social smile is formed with a different configuration of muscles from the genuine smile of pleasure. A social smile is executed by circuits in the cerebral cortex that are under voluntary control; a smile of pleasure is executed by circuits in the limbic system and other brain systems and is involuntary. Anger, fear, and sadness, too, recruit muscles that can't be controlled voluntarily, and the genuine expressions are hard to fake, though we can pantomime an approximation. Actors must simulate facial expressions for a living, but many cannot avoid a mannered look. Some great actors, like Laurence Olivier, are highly coordinated athletes who have doggedly learned to control every muscle. Others learn method acting, inspired by Konstantin Stanislavsky, in which actors make themselves feel an emotion by remembering or imagining a charged experience, and the expression pops on the face reflexively.

Probably this is what has happened: the stroke has affected my voluntary muscles making it difficult to produce a polite smile but since my involuntary muscles are working fine, spontaneous laughter is easily produced. I have used this Stanislavsky method for years without knowing why I had to do so. Often when I had to smile politely, I tried to think of some joke which will make me laugh and everyone will think I laughed because of what they had said.

You see the problem with this post, don't you? Now everyone who comes to meet me after reading this post will have a nagging doubt in his mind - Is this guy's laughter genuine or is he indulging in a bit of method acting? H'm, I can see some uncomfortable meetings ahead.