Er, that sounds kinda immature, and a mean thing to do to someone. Besides, I doubt people would spill their deepest secrets even if they were dreaming, but I suppose you never know... Anyways, I have no personal experience, so I can't say much. I dunno why it wouldn't be possible (assuming SD is possible in the first place, of course) but... think carefully about it. They might not find it as funny as you do, ya know.