The Government Is Transmitting Thoughts Into Our Brains!
This is the stereotypical "tin foil hat" conspiracy theory that the government has the ability to beam thoughts into or out of your skull using its Illuminati mind-ray technology. This is a favorite of crazy people because, well, they're crazy, and hearing strange voices in your head is as common a symptom of craziness as you'll find. Assassins Mark Chapman and Sirhan Sirhan both claimed to hear voices in their heads telling them to murder their targets.
You can use the same excuse to get away with stealing lunches from your co-workers.
But they're not the only ones who have ever claimed to hear voices broadcast directly into their heads. All over the country, people who aren't murdering beloved public figures have also asserted that the United States government is trying to control their minds by transmitting thoughts directly into their brains. Which is why some of them elect to don the aforementioned tinfoil headgear -- to keep the voices out. This is why the tinfoil hat has become the emblem of all things conspiracy-related, mocked in movies and elsewhere.
ProTip: Make sure you remove the leftovers from the tin foil before putting it on your head.
Why It's Not So Crazy
They can totally beam voices into your head.
In 2006, a guy whom multiple counselors labeled as a "paranoid schizophrenic" filed a Freedom of Information Act petition requesting all declassified government documents pertaining to covert attempts at microwave auditory effect, telepathy and hypnosis. While no one was surprised that a guy who once complained that the backs of his shoes were vaporized by an electromagnetic weapon would go through the effort of filing the request, a lot of people shit a brick when they saw the papers that came back.
Page after page of verified government documents confirmed that taxpayer dollars had funded research on everything from a telepathic ray gun to fever lasers that made victims disoriented and less aggressive. And, yes, one of the released tests even broadcast a person's voice telepathically by "using close-range microwaves ... to project the spoken numbers 1 to 10 across a lab to volunteers."