Sex, drugs, piercings, tattoos. (The worst is tattoos, but it's too late now.) Most of us will not die of an untidy bedroom, but it is nice to think that.
Most teenagers will experiment with sexual behaviour at some stage – this is a Some teenagers are sexually attracted to people of the opposite gender, some.
Curiosity / Experimentation. Most adolescents are curious about sex. Some of them will take advantage of an opportunity to find out more—with younger children.