Folding your three middle fingers down while holding out your thumb and pinky, then twisting your hand around, is a strange gesture to say the least. But if you visit Hawaii, you're likely to see it a lot. The gesture, called The Shaka Sign, can be interpreted as "Hello," "Goodbye," "Have a nice day," "Take it easy," "Good luck," or, the most popular definition, "Hang loose." Unfortunately, the sign's history is a bit vague.
The oldest origin story goes back to the days when Spanish sailors first landed on the Hawaiian Islands. Unable to speak the native tongue, but trying to be friendly, the Spaniards offered to share a drink by mimicking a bottle with their hand with the gesture and tilting back their head. This became such a common greeting that the natives simply believed that's how the Spanish said hello, so they started using the sign whenever the two groups encountered one another.
Another theory, from the mid-20th Century, claims the sign was inspired by the wave of a beloved local named Hamana Kalili, who'd lost the middle fingers on one hand. There are multiple theories as to how he lost his fingers: there was a shark attack, they were blown off while using dynamite to catch fish, or perhaps the digits were lost in an accident while working on a sugar plantation. But no one knows for sure anymore.
As if the origin of the gesture isn't mysterious enough, the word Shaka isn't even Hawaiian. However, most people agree the name goes back to a local used car salesman, Lippy Espinda, who would throw up the sign at the end of popular TV commercials during the 1960s and 70s, and say, "Shacka, brah!" ("Shocker, bro!").
(From mentalfloss.com)