All the other definitions of wristy are wrong. The wristy is actually sort of a "high-five" alternative where one bends his/her wrist about 45 degrees, also making a very slight fist, and makes contact at the wrist of another person doing the same thing. Used to celebrate the mention of the number five, a shared amusement, or a mere agreement.
Josh: Yo, I'ze about to get me FIVE delicious BURRITOS from CHIPOTLE!
Chris: Yut! *wristy, both for the five and the excellent choice of CHIPOTLE*