Please, share more white secrets. 
I've never seen the things Mupepe and Atramental are talking about but I have heard about it.
I think a lot of it is regional based.
A white secret is fluid ethnicity. We all know someone who claims to be 1/8 Indian but it applies to other ethnicities as well. One time you'll hear a cac talk about their Irish roots and then six months later they will talk about their Italian roots. Often times this coincides with holidays and which ethnicity complements it. Rachel Dolezal going transblack is not really surprising when you really think about the white concept of fluid ethnicity. I mean, if there is some guy who is ginger, his name is Patrick O'Malley, and talks about being Irish, then yeah I believe it. Most white people in America (80-90 percent) are a mix of many other peoples and countries and as such, have no real claim to a specific country. Since they want to identify with a country, they will just make it up to fit in.
What I'm saying is the next time some white man/woman talks about being from <x> country, assume they are full of shit. However if you call them out on it, they will get pissed off, which is usually a sign that you've caught them in a lie.
Edit: Another item to speak on regarding this is that there is one common ethnicity that most cacs are loathe to identify as:
https://en.wikipedia.org/wiki/Scotch-Irish_AmericansThis is probably what they mean when they talk about coming from Ireland or Scotland. The reason why cacs hate to consider themselves these people is that they were known to be rowdy shitkickers. SWPLs who obsess over this kind of thing don't want to be known as people who descended from the same people who reside in Appalachia but it's true! It's not a SWPL/hipster friendly ethnicity.