I do not know how to post images, but if you try to order a shirt from osu!, it says "NOTE: Sizing is US standard sizing. If you don't live in the US, you probably want to order on the small side." My theory is that a lot of Americans are overweight, but the clothing companies do not want to make their customers feel bad (and not want to buy their clothes), so they would label their shirt sizes as smaller than they actually are, but other places don't do that. I don't want to offend or fatshame anyone, but I just thought the note was kinda funny (and useful.)