Just as men aren't supposed to wear hats at the table, women aren't supposed to "powder their noses" or apply lipstick either. Most of you think that applying makeup in public [1] isn't so cool, but I've consulted Emily Post [2]'s (queen of all etiquette) website for the official word on manners. As it turns out, there's no one right answer:

• Why it's a yes — "In general, personal grooming should be done in private for the simple reason that it can be annoying and it’s tacky," Post explains. "Still, think first! When in doubt, don’t do it, such as when you’re at a business meal or with people you don’t know very well."
• Why it's a no — According to Post, "It’s okay to quickly apply lipstick at the table if you’re with close friends or relatives in a non-business situation, and at a non-deluxe restaurant."
• Why it's a maybe — "Put putting on lipstick without using a mirror and without fanfare is one grooming ritual that can sometimes be performed in front of others," Post says.

So, depending on where you are, you're just fine — no need to freak out if you need a little touch-up.

Source [3]