So.. how do you know whom a tap is from? Let's say you agree that three taps means lunch with a specific colleague. What happens when someone else sends you three taps? Every time you get a tap notification from someone you need to look at your watch to see who sent it, and then remember what it meant for that person. The more people you use this with, the harder it gets to agree upon unique taps for that particular person and occasion. Saying "oh no, we can't use three taps, because I'm already using that with someone else" only works so many times. And what's stopping people from annoying you with constant tapping? Kind of like being stuck in a pre-iOS8 iMessage group chat you can't get out of.