I was trying to see how much of the writing on the signs in the park I could make sense of today and found something of interest.
A sign stating what not to do in the park covered not littering and in that section was the turn of phrase
I could find the meaning of ポイ online but so far not its origin. It means "throwing away" or "littering".
As it's in katakana I tried to think of an English word it might be based on but couldn't think of anything. Of course not all katakana words have origins in English.
A local friend suggested it could be one of Japanese's famous "onomatopoeia" words. But it seemed to me that just about all of those I'd come across are two syllables with reduplication, and written in hiragana.
So from whence ポイ?