What it is
Doctrine as costume is when a principle made for one purpose gets bent to license a grab that was decided in advance. Free speech, religious freedom, property rights, national security: any of them can be worn this way.
The tell is that the doctrine changes and the outcome doesn’t. Greed is the constant. The principle is interchangeable.
How it shows up for me
I try to apply this to my own side too. If I only care about a principle when it gets me what I want, it’s not a principle, it’s a costume. That’s an uncomfortable test, and I fail it sometimes.