Unprincipled nihilists cannot betray themselves because they have no principles to betray

We betray ourselves when we betray our own principles. But what should be our principles?

If we have a religion, our principles would be our religious principles.

If we are atheists and seek to be known as moral, rational and honourable, the we would have to submit to Truth, Logic and Morality and be prepared to engage on the truth, logic or morality of the thing until it is resolved.

Unprincipled nihilists do betray themselves when they say they make a point of having no principles. What loving father would allow any daughter he loves to marry an unprincipled nihilist?