also: でこピン
noun
finger flick to the forehead
A playful or teasing gesture where one flicks someone's forehead with a finger, often producing a light popping sound. Common among children or in casual settings.
弟にデコピンしたら、泣いちゃった。
When I flicked my little brother's forehead, he started crying.
デコピンって結構痛いよね。
A forehead flick actually hurts quite a bit, doesn't it?
A compound of でこ (slang for 'forehead') and ピン (mimetic for a flicking sound). The exact origin is uncertain, but it likely emerged as a colloquial term for the playful gesture.