The guy who put up the sign correctly assumed that the lazy people he targeted would (irrationally) react by paying more attention. Which was the desired effec

The guy who put up the sign correctly assumed that the lazy people he targeted would (irrationally) react by paying more attention. Which was the desired effect. Recognizing (and exploiting) irrationality in others may be a bit mean, but its definitely not irrational by itself. Now, there may be a simpler explanation: people see the angry note, think "Oops, someone cares about this crap", and change their behaviour just to be nice. Or maybe they just didn't really know how they were supposed to handle the trash, and the note made them less ignorant. Personally, I suspect all three effects played a part.