"Can't someone else do it?" - Homer Simpson

Ah, you're describing Moral licensing, and that's entirely plausible.

In this case it's "Littering is bad, but there's no trash cans here and I'm a generally good person so, just this once."

Except I suspect that "once" is really "every so often."

I always thought it was "it's just one can/bag/bottle" when its clean, "it's full of trash, one more won't make a difference"