I found this great post card at Garden Books in Shanghai (nice selection of English language books in the French Concession). The description reads: “Sticking the tongue out as a Tibetan greeting began when Buddhists wanted people to know that they were not Bon-Po (pre-Buddhist religion) as they were supposed to have black tongues. Pink tongues were stuck out as proof of being Buddhist. The further the tongue out, the greater respect. It is still seen today.” Does that make Mick Jagger Buddhist?