Used to do this all the time in church. I'd be listening to the sermon, and all of a sudden realize that the minister is simply repeating what I had just thought. I've also done it one-on-one with some of my acquaintances. Out of the blue during conversations, I'll occasionally say something that doesn't seem to follow the train of thoughts of the conversation, and they'll look at me a little strange before asking how I knew that they were about to say/ask that. Luckily, everyone who I've done it to so far has been very mature about it, and not asked me to read their minds, or anything stupid like that.