How Do Theists Know That God Communicates With Them?

Recently I had a discussion with a religious friend and asked him what I consider to be a key defining question. I've tried to record the dialog here as accurately as I can, but obviously the following is not a transcript. During the course of the conversation the "relationship" topic came up.  Knowing that communication is an important part of a relationship I asked him "Does God talk to you?".

Does God talk to you?
He said "Yes".
I said "When?".
He said "Right now."
I said "Well, what's he saying?"
And he said "He wants you to know he loves you and he wants you to come back..." yada, yada, yada.

So I said "Harvey, my six foot rabbit friend standing here next to me says he doesn't believe you".
He laughed. So then I said "God, did you really say that?". Of course there was no answer.  Then I said to my friend, "That is exactly what I would expect to happen if he wasn't really there. You don't believe in Harvey, and if you ask him a question, he won't answer.  Either he's ignoring you, or he's not really there. You decide. But seriously though, how do you know the difference between the thoughts that normally occur to you and the ones that you think come from God?".
He said he didn't know, but he could tell the difference. 

What is the difference?
I told him that I thought he was just making stuff up, and that he didn't really know what was auto-generated by his brain and what came from God.  My point was that if there is no demarcation, no point of delineation then it should all be assumed to be auto-generated.  The reason why, and to draw a loose analogy, is that until a schizophrenic learns what schizophrenia is, they are quite certain they are interacting with voices and persons that are auto-generated by their brain.  And to a lesser degree, I know people that hear things that aren't there, I know I do, and I know that when I was in a band, under certain conditions I could hear a bass line that I would "copy" and use in our original songs. 

No one could hear the notes but me. That wasn't supernatural, I am sensitive to frequencies in a way that others aren't and I am quite sure that a spectrum analyzer would be able to detect them. Now that I'm older, when I'm in a noisy industrial environment, I can hear "beats", "partial melodies", "phones ringing", "voices", you name it. If it kicks off that portion of my brain that recognizes a sound, whether its the real sound or not, I hear it.

The Difference is Easy to See in Most Other Cases. It Can be Cross-checked.
This problem of differentiating between what is auto-generated and what is perceived is easy in all other cases.  When I communicate with people, I see it, or hear it.  It comes in through my eyes, ears etc. I know how I perceived it. The source of the information is known, and it is usually of a sort that is generally independently verifiable. It can be cross checked.  I don't have to resort to special pleading to get someone to believe that I have perceived the communication.  If I tell you that my friend told me something in the course of our dialog and if you knew who it was, you could ask him.  When I told my band mates that I heard the notes, then immediately played them, the possibility that hearing the notes might be supernatural never occurred to them.  We all understood feedback, resonance and harmonics so that was adequate to explain the way I could come up with the perfect bass line after listening to the song for a minute.  If it was from some spirit, let them take the bass out of my hands and show me like any other person would. A spirit appearing before my eyes and giving me a bass lesson would be incontrovertible evidence to me.

Not So With Gods.  
As I pointed out to my friend, if I ask God if he really said that to my friend, I don't get an answer, and other religious people are just as certain as he is that they have a relationship with their Gods, and when I ask those Gods to talk to me, they don't either. 

Special Pleading and Disconfirmation Bias
If God exists, and he talks to my friend, then my friend should be just as willing to accept that any other God exists, or that Harvey exists on the same grounds.  If not, then he's committing the fallacy of special pleading to support what he already believes and ignoring disconfirming evidence aka Disonfirmation Bias.