I try not to smoke with my folks at home, period. If I do, I usually wait till they've both gone out or fallen asleep for the night.

If I really have to, though, I smoke in my room (locked, smoke out the window and sock over the fire alarm) or in the bathroom (no joints, because the extra smoke gets caught in the curtains).

That's always really shady, though, and I'm generally paranoid for my whole high--a wasted experience.