1. V.- The ability to fit a finger or fingers into one's own ass, up to the second knuckle. Traditionally used for sexual pleasure.
2. V.- To insert a finger into someone elses ass up to the second knuckle.
Dude, I'm totally a double knuckler what about you?
A descriptor for a beautiful woman or man, meaning the act of biting the middle knuckle of two fingers of a closed fist at the sight of beauty. Biting one finger would be a "single knuckle", biting two is a "double knuckle".
Did you see the new cashier lady at Safeway this week? Man, she's a total double knuckle.