For those tempted to argue about the impracticality of implementing my tongue-in-cheek mockup:
Imagine, instead of the silly alert message, a simple toggle in privacy settings “allow others who have me in their contacts to share my information with apps”
If it’s switched on, it flips a bit on a server that the other person’s OS can check, just like how it checks if you’ve set up iMessage etc.
The point wasn’t the UI, it’s that other people’s info shouldn’t be yours to give out to apps