I want to smoke a cigarette to feel better. I want to smoke opium to feel better.
I think we can ignore the consequences of everyone performing this action (in similar situations), mass addiction and endemic cancer. But everyone getting high on opiates is an undesirable result, even if it's conceivable for it to occur: an imperfect duty.
What about taking LSD to expand your mind? I think I may have a perfect duty not to do that, depending on whether the doorways of perception are relative (if we cannot all have "expanded consciousness"). The sort of perfect duty which is explicitly written into language, like lying as opposed to e.g. murder.
What about alcoholism? I struggle to practically conceive of everyone being an alcoholic (who would make the wine?), deliberately drinking themselves to oblivion, so it's a perfect duty not to do that?