I know I rant about this quite a lot, there's nothing more annoying for me than being served a full sugar soda in a restaurant when I've obviously ordered diet. In my opinion, not only is it bad service but it's also dangerous because I'm a diabetic! Of course I understand that we're all human and people make mistakes, but it's happened to me so many times.
Because this post is about designing my dream diabetes device, I have designed The Amazing D-Straw! Basically when you put it in your soda, if it is diet it will turn to blue. If it's not it will turn to red and then you can demand a refund or a swap! Just be polite when you ask for a swap, the last thing you want is a fed-up barman spitting in your soda to teach you a lesson. Ewww.