Pretty basic, really. City has trashcans everywhere, so one is bound to run into one eventually. It costs literally just as much effort to shove that wrapper into your pants pocket as it does to chuck onto the street.
Yes, if a) you were raised with such values? Common sense? Both? And b)if your city has a lot of thrash cans. I'm surrounded by a lack of both so the meme is accurate to the folks that keep trash in their pockets until they get to a trashcan.