When I was younger, I never had imaginary friends per se. Instead, I would imagine teaching a room full of kinds or so or play with Bun-Bun and pretend he was alive (think: Calvin and Hobbes).
<--- That is Bun-Bun by the way. He's been through a lot of wear and tear, so go easy on the poor guy.
I used to make fun of people who ACTUALLY thought imaginary friends were real, as I always had a clear distinction in my head what was 'real' and what was 'goofiness to entertain me.' It wasn't the MAKING the friends that was so foreign to me as the inability to distinguish reality from fantasy and then forcing others to accept it.
For example, once when I was 10 or so, I saw a free swing, and very politely asked the girl next to it if it was available. She said, "No my imaginary friend is on it." At first, I thought it was a joke, so I laughed, but she shrieked and said, "YOU'RE SO MEAN; YOU PUSHED SARAH OFF THE SWING!" And I looked at her incredulously and said, "Are you feeling okay? There's no one there!" And she said, "Sarah is on the swing, and I was saving it for her." I muttered something like, "Psychoooo" under my breath, sat on it, and said with some indignation, "Well, then tell Sarah to play somewhere else!" After which time, the girl ran away crying to her friends, and her friends came to me and said something like, "You're a bitch!" And I said something like, "What am I supposed to do? LIE AND PRETEND something is there when there is a swing available???" I was visibly perturbed, and I saw that as a completely unfair way of them to put a stage on so that I wouldn't "invade their space." Well, fuck you and play somewhere else then, if you can't put up with me. Shut it. If you can't deal with the heat, get outta the effing kitchen. There, look, there's the door. Psychos. I'll never forget it.
On the other hand, I had no problem going home and 'studying' by pretending to have a discussion with Hitler. Or by teaching a room of imaginary kids what I had learned. Or by thinking out loud. But it was always clear (and I can't stress this enough) that the imaginary thing in my mind WAS NOT real - that it was simply a projection for a purpose.

Maybe I am a sensor.