go and post a letter or something, skin up in doors then go and stand in the garden. if its night time and your parents are asleep go and 'investigate' the noise outside!!!! something like that, if your sure they wont come into your room smoke out the window.easy peasy
make a lung. i think thats what its called. i have one, just a waterbottle stuffed with a bunch of toilet paper that i've sprayed with axe. then, poke a hole int he other end and exhale through that. covers smoke and smell. of course, stuff the towell under door, have axe on hand, a little bit of music to cover lighter sounds/whatever. and chilllll.