This is priceless. Justice Breyer defines rational basis:
we can imagine a reason, but if you look at it realistically, you know there's no good reason.... I mean, if you put your mind to it, you can make one up, which is sort of the test for rational basis in the economic context. But as soon as we become realistic, there isn't much of a reason.
In other words, as Clint Bolick is fond of saying, the only two things you need to know about rational basis is that it does not have to be rational and it does not have to be the basis.