This is a real issue in daily life for a lot of us.
The response,none of your business,will work but then the agent, cop, whatever will have to prove they are your superior, at least in their own mind.

There are several other ways to get them out of your business such as saying your lawyer has instructed you not to answer questions without he,she being present. This way is a little less confrontational. You can also ask if you are under arrest or detention and for what purpose. If you are handcuffed or ordered into another area you are detained and should shut up. Complete silence really frustrates them to no end.

A third tack is to reply off the subject like "nice weather for this time of year isn't it agent?" Just don't talk complete nonsense as this will give them the opportunity to put you on a crazy hold in the local hospital.

Sorry but Lukacs is an idiot. He's trying to make this incident into something that it wasn't and doesn't even have the basic facts straight regarding civil rights and law enforcement. What he'd experienced was entirely legitimate under due process. He'd refused to answer a compulsory question, and so was detained and investigated. Then he was released when it was determined that there wasn't further cause to detain him. That's due process. There's no interpretation of these principles that allows a suspect individual to determine whether they wish to be the subject of an investigation.

Consider an example from law enforcement. You fit the description of a wanted individual. A police officer approaches you as asks, 'excuse me, are you Suspect X?'. If you say, 'I refuse to answer that question', the officer is perfectly within his rights to detain you. This isn't even an arrest, simply detention in pursuit of an investigation. That's how it works, always has.

Mr. Lukacs is a minor hero of the Restoration whether he knows it or not. The reactions of the CBP sockpuppets and fellow travelers give us a glimpse of just how much anger even a tiny act of defiance can trigger. Completely out of proportion. Those people are simply not sane any more. If they ever were.

Searches of your belongings are allowed at the border without any cause at all.

Searches of your person require reasonable suspicion that something illegal will be found (i.e., a concrete and articulable grounds for such a belief).

(Unrelated: at Lukacs' blog, he says "CBP officers treat returning U.S. citizens as potential criminal defendants. You should likewise treat them as if they were corrupt cops on a power trip, targeting you to goose their arrest statistics. The best way to protect yourself against their depredations is to refuse to speak to them or to answer their questions."

Well, I've crossed the border a lot of times.

And while they certainly do - as they should - ask question that are aimed at ferreting out smuggling and the like, I've never encountered the attitude he claims.

Oh, I've had them ask me if I was doing any number of illegal things, but that's the only way to catch smugglers outside of random searches.

Not because smugglers are stupid and say "yes, I am carrying illegal stuff", but because their cover story is much more likely to not hold up to repeated asking of "where are you going?" and "do you have any X?" than an innocent person's perfectly honest answers.

He thinks that's "treating him like a criminal".

I think he's overreacting and has no idea how people they really think are criminals get treated.

And as to "trying to goose up arrest statistics"?

Hell, I once didn't declare a bottle of liquor [because of a confusion about "acquired outside the US" declaration vs. "declare everything we might care about"], and ...

I was not cited or arrested as a smuggler, or made to pay duties!

He said it was obvious I wasn't trying to do anything illegal and sent me on my way unmolested, perfectly politely.

Mr. Lukacs would seem to be wrong about, well, every CBP agent I've ever had to deal with.

Refusing to answer their questions, so long as the questions are perfectly reasonable ones along the lines of "how long were you in Country X?" and "are you bringing back any Y, Z, A?" simply makes him a jerk with an entitlement complex.

He'd refused to answer a compulsory question, and so was detained and investigated.

miikiik, mordez moi.

There is no such thing as a compulsory question anywhere in the U.S. Constitution. In fact the Fifth Amendment (No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.).

The moment you talk to a government official you are subject to the the Fifth. That is the same reason that the Miranda warnings were judged to be so important to the court.

I have an incident in my past that I should have not said a word to the deputy -- I talked and had a minor conviction. If I had remembered the words of a good defense lawyer or the link Amy has above I might be better off now.

He seems to forget that the USG is under no obligation to issue him a passport and can revoke it at any time.