A、In movies. B、In real life. C、When people want to say OK. D、Anytime. A

To wave goodbye or hello to someone, raise your hand and wave it from side to side, not front to back. Wave the whole hand, not just the fingers. Waving the hand front to back or the fingers up and down means "no", "stop", or "go away". Holding your hand up with the palm facing forward but no movement means "stop". Holding your hand with the palm toward your body and wagging the fingers toward the body means "come here", Holding your hand with the palm up with all fingers curled and repeated curling and uncurling the index finger means "come here".
    If you want to point at an object, extend the index finger and use it to point at the object. It is not polite to point at people.
    If you want tile waiter to bring tile check, make a writing gesture with one band as the pen and the other hand as the paper. If you just want the waiter to come, make eye contact and raise your band.
    Shaking your head from side to side means no. Shaking your head up and down means yea. Never show your fist with the middle linger extended. This is an insult. Shaking a closed list at someone is also rude, especially if it is in their fane, and is an expression of anger.
    Although showing your fist with the thumb up or your open hand with the tips of the thumb and index fingers together forming an "O" means "ok", this is an overused stereotype. Americans understand this gesture, but it is mainly used by actors in movies, not in real life.
    It is nut polite to pick your nose or chew your fingernails in public. Likewise, it is net polite to pick your teeth (with or without a toothpick) in public.
    In some circumstances a wink will signal amusement or that the speaker is kidding. Because of the potential for misinterpretation, winking shoed be avoided.