Rhetorical questions like "do you know how bad this is?" are not very constructive. People know how bad smoking is and what the consequences are, so harping on them is mostly redundant. Maybe it's just human nature to repeat, state the obvious and want agreement even in the bad things -- especially when a point doesn't seem to be getting through.
Another reality is that the negatives for a nonsmoker are probably not as negative to someone who smokes. Sense of smell is masked a lot when a person is smoking, so telling someone over and again how bad it smells isn't likely that effective because to many smokers, the smell of cigarettes is familiar and comforting. Most people who once smoked notice a drastic change in how bad cigarette smoke smells after they quit, but while smoking, the odor is not much of a reason to quit [source: NIH].
Constantly harping on the financial costs of smoking also does no good. Cigarette prices and taxes have steadily risen, but one out of every three people in the world still smokes [source: World Bank]. So is all of that harping about money effective? Gauge the expressions on your loved one's face next time and consider a positive turn of phrase -- some things to be gained in quitting -- instead.