I don't think anyone would argue that homeschoolers aren't smart. I agree, they're better at talking to adults as adults too. It's when you you get them around a group of people their age who aren't at a church / homeschool function that you notice it. They're generally just a little weird.
For what it's worth, I spent the first year or two of college just figuring out how to interact with "normal people" my age. It's little things, like how they resented me for using words they didn't understand.
Maybe being a huge nerd contributed to it as well, but whenever I blame something on being homeschooled (i.e - I still can't get the cool hand shake / fist bump / flippity-flop thing down that people do), it almost always surprises people. "Really? I would have never guessed," Is a common response. Because, like it or not, most homeschoolers are obviously homeschoolers.
