When in Rome Tibet…
Why? Via LA Times:
In the movie, “Seven Years in Tibet,” the Brad Pitt character encounters a group of Tibetans who all at once stick out their tongues at him. No explanation is offered, but this custom has a long history.
A 9th century Tibetan king, Lang Darma, known for his cruelty, had a black tongue. As Buddhists, Tibetans believe in reincarnation, and they feared that this mean king would be reincarnated. Consequently, for centuries Tibetans have greeted one another by sticking out their tongues demonstrating that they do not have black tongues, that they are not guilty of evil deeds, that they are not incarnations of the malevolent king.
This custom reportedly derives from a belief that demons have black tongues, and sometimes that is all that differentiates them visually from humans. A demon won’t stick out its tongue in greeting because you’ll see the color and know it for what it is.