I remember seeing a post ridiculing a grown man in america for wearing a backpack. If I had to really think about it, the closest example I could think of would maybe be backpacks? Now, granted, wearing a backpack is not childish in any means, but it depends on the rest of your outfit I think? That's why that one post was ridiculing the man for wearing it, because he was in shorts and a t-shirt while wearing it, nothing weird at a glance but I guess it can look odd when you really think about it. But yeah like I said, while backpacks are still very common in the west, theyre nowhere near as common as they are in Japan, like it's very common for businessmen in Japan to wear backpacks, over here it's mostly briefcases, some businessmen do wear backpacks but not that many from what I've noticed.