Sprick is a term from my school days, junior high. Using your thumb, you held back your finger, tensing it up, and then, when you loosened your thumb, your finger snapped out at its target, the earlobe of the person sitting in front of you for example, causing sharp pain. I was usually on the receiving end of this.

This is also how you flick a paper football. But we called it sprick rather than flick, probably because it sounded less friendly.