In the category of "care and feeding of mrissas": I will shake hands with people, I will hug people I know, I will try to assume the best of people even if their idea of casual friendly contact isn't the same as mine. I try to deal with people from interruption cultures and people with long conversational pauses as gracefully as I can. But one thing I do not tolerate well is people telling me to smile. If you aren't taking a posed picture, just don't. Every Northern girl* learns the smile that means, "I will commence bashing your head in with a large stick in ten...nine...." Do not solicit this smile. You will not enjoy it if you do. Especially do not put this order in terms of girls/women being prettier when they smile. This will move the countdown forward.
*People of other genders and cardinal directions may learn this smile as well. I don't know, not having grown up as any of them.