Here’s a story I heard a long time ago about syphilis. I don’t know if it’s true: you tell me, Dear Reader.
You know how posh little old ladies and flamboyant gay men like to hold their pinkie finger in the air when drinking tea? This is because of syphilis at the court of Louis XIV in 17th century Paris. Those people were severely pox-ridden. And they were the cultural elite of their time, emulated in every detail of dress and behaviour by Europeans everywhere.
One thing syphilis does to you is damage the joints of your fingers. After a few years, you are no longer able to bend your pinkies. When holding a glass or cup, your pinkie will point ineffectually at the ceiling. Non-infected people won’t readily understand this, and even if they do understand, they may see the pinkie thing as a typical trait of your poxy social circle. If they admire you enough, they may go home from your splendid court and start doing the pinkie thing even if you have not managed to infect them with syphilis. Call it a meme if you like.
The guttural French R sound has been gaining ground in European languages since the 17th century and is currently typical as far north as the Swedish province of Småland. There is a hypothesis that this linguistic trend was started by a single very influential person with a speech impediment, somewhere in France. Perhaps the man with the pinkie?