Sex...well most people I know lose / lost their virginity around junior year of high school. Unless of course you're really religious, really prude, or you're just ugly. Or all of the above, which would really be terrible.
As for smoking, um, too many people smoke marijuana for you to be able to hate anyone who smokes that, but I agree, cigarettes are pretty gross. On the flip side though, the average salary of people who smoke cigars is upwards of $300,000.