I would like to run a breeding farm for girls with smelly feet. Truncation selection: take the top 10% of girls with the smelliest feet; breed them; repeat. Within 10 generations or so, I bet the girls would have really, really stinky feet! I'd bet they couldn't even stand to be around each other because it would smell so bad. Merely taking a cotton swab and swiping it across their bare soles would be enough to construct a biological weapon capable of wiping out tens of thousands of people in an urban environment.