Is it true that everyone would know a sociopath?

Of course. Technically, everyone in high school is a sociopath. The reason the sociopathy test isn't given to adolescents is that adolescents who take it almost always score in the positive range for sociopathy. During the ages while the frontal lobe is developing and maturing, which starts in early to mid- teens and doesn't fully complete until about age 21, people who take the APA diagnostic test for sociopathy get results indicating they're sociopaths with near unanimity. So if you've ever thought teenagers seem like little sociopaths, know you were completely right.