I recently moved into the dorms for my senior year of college, and everyone's door has a piece of paper with their name on it. One person has 'John' crossed out and 'Jack' written underneath.
This is pretty common where I'm from--Massachusetts. I've known about four or five guys named John who went by Jack. John is also really popular here, more so than most places--2018 was the first ever year it wasn't a top 10 name.
But I've seen people online be very confused by this nickname.
So--where you're from, is this a thing? What do you think about it?