Littering with

ポイ捨(す)て is short for ポイと捨(す)てる. It refers to littering small pieces of trash in public places such as streets and parks.

Usage Notes

ポイ suggests tossing something aside casually. The word commonly refers to small litter such as cans, bottles, wrappers, and shopping bags.

Further Reading

Examples

Littering a soft drink can with ポイ捨て

Manga panel from ふだつきのキョーコちゃん showing example of Littering a soft drink can with ポイ捨て.
ふだつきのキョーコちゃん » Volume 2 » Page 47

As Kenji Fudazuki ponders ways to increase his image as a delinquent, he hears a teacher asking who littered an empty soft drink can. Seeing an opportunity, Kenji takes credit for the misdeed. With this revelation, the teacher backs off and leaves quietly.

Students:
「札月(ふだづき)だったのか。」
“So it was Fudazuki, huh?”
「しかしポイ捨(す)てしといて全(まった)く悪(わる)びれてないぜ…」
“But to litter, he really has no shame...”
「むしろ怒(おこ)ってた先生(せんせい)ニラんでたぜ。」
“Instead, he glared at the scolding teacher.”
「ホント…怖(こわ)いなぁ。」
“He truly is scary.”