I actually called someone on the litter they dropped one day last week. I did it without thinking, but she was walking towards me, dropping the wrappings from her sandwich, and when she got near me, balled up a piece of paper and threw it purposefully on the floor in front of her, I just reacted and said 'hey, there's a litter bin right there!!!' and, arm thrust out, finger pointing at a litter bin I hadn't realised was there! She just looked at me and kept on walking...
It's been my pet peeve since the first Earth Day in the US...
(BTW, PeterPerfect, had to laugh, I didn't think you were going to continue that sentence beyond the word 'heave', although I know that's true too!)