Lang Darma. Good manners to stick out your tongue in Tibet

In Tibet it is considered good manners to stick out your tongue at someone. 

There was once a cruel king in Tibet named Lang Darma who had a black tongue. Tibetans believe that this king will be reincarnated. Therefore, they greet each other by sticking out their tongues, to prove that they are not the reincarnated evil king. This tradition has gone on for centuries, so now it just serves as a customary display of respect.