I’m a white person, but of course that’s not the sum of what it means. In the contexts I have read, it means a white person who is stupid about their white privilege.
I try to be aware of my white privilege (and male privilege), but it’s not top of mind all the time, and I suppose I might do or say something clueless sometimes. One thing I do know is that, being white, I don’t have to carry the fact of white privilege in my head every minute of every day for survival, like some people of color do. On that account, at least, I am inclined to cut a lot of slack in the use of that expression.
I will add that I don’t find it particularly helpful, and if I did find myself lumped in with people who don’t behave well only because of my skin color and not because of my own behavior, I would discount its validity as a piece of social intercourse. On the other hand, some white people (along with some other people) deserve to be laughed at, which is what this seems to be mostly about.