This is probably the trickiest achievement in the game, but just requires a good strategy to obtain(and a small amount of luck). You need to serve 5 coffees in a row, without serving anything else. This is easier to do when you have a 4 or 5 star rank in London as you will be getting more customers to serve at a time. Basically, you just need to go about serving as normal, except that you need to ignore all requests for coffee until there are at least 4 customers requesting coffee at once. While your are serving those four coffees, another customer will likely request a coffee for your fifth. The coffee machine only makes four at a time, so you will have to make more to serve the fifth person. Make sure you have the difficulty set to Beginner for this one, as it will reduce the decrease of your customers hearts while you are waiting to serve them coffee. You need to reach 3 star rank to unlock this destination.