'慢慢吃' (man man chi or eat slowly). I feel uttering this term at the end of a meal, when you have finished eating earlier than others, lets your Chinese friends/relatives know that you are no longer a ordinary '外国人' (waiguoren or foreigner) who is to be taken lightly. It tells them you're ready for Chinese culture and you mean business! :) 

By the way a very helpful article!