In Canada and the States, I think it is customary for us to dump our junk after we're done at McD. But in HK, I'm pretty sure the common practice is the opposite, and the clean-up uncles and aunties will come clean up very quickly afterwards.
i don't eat there really~
but if i'm at a fastfood place~ or food court place~ i am used to cleaning up after myself~
half of the time when i'm at a restaurant~ i'd stack up my dishes in such a way that it's easy for the people to take away afterwards~ that's just a habbit of mine~
i personally think it's not the act of not throwing it out is the problem~ i think it's the attitude~ i have had people told me that if we are too clean and tidy~ then those people who are hired to clean won't have a job~... kinda twisted still~ but i think that's more acceptable than.. 大爺是來這花錢的 that kinda reasoning.