Which is a very easily recognized pattern, color, and size. The entire point of a dollar is that every single one looks identical.
Imagine if every single dollar bill was a different color, shape, size, printing pattern, etc… Now imagine trying to block that. Now consider that as soon as you figure out how to block all of the current versions, anyone in the world can just design a new version in 5 minutes.
I can guarantee that private school kids do the exact same shit as public school kids. They just have more money, so they can get into more expensive shenanigans, and their parents are able to smooth it over with the cops/lawyers better afterwards.