I used to communicate the Church's teaching on human sexuality to teenagers from a position of fear. I find that most adults do this when talking about sex to teens. They don't do this with any other Church teaching. They don't use scare tactics when talking about the Eucharist, or even Hell for that matter (if it is ever taught). When sexuality is involved, though, the fear comes out in full force.
The fear that I am talking about is not nervousness while dealing with a sensitive subject. My dad had that kind of fear when he told me and my older brother about the birds and the bees. He was terrified. He used the technical terms for things that were completely over my head. I would just stare at my brother's face and when his smile turned to utter disgust, I would just mimic the same expressions. "Ewww that's gross!" my brother would say. "Yeah, umm, gross!" I would quickly second. The best part? He gave us the talk by putting us in the back seat of the car as he addressed us through the rear view mirror.