Smokin weed around your plants is kinda like a cannibal eating someone in front of you, makes them feel all queasy and sick. Truthfully, I have no clue.
It's not rocket science. Marijuana grown best with fresh flowing oxygen. if you decided to blow smoke at your plant while your stoned, it won't do much but it's not good for it or anything. C02 is only to be used during the dark period of the light cycle.
yeh i have wondered this myself before...my plants are in my room though so not really any way around it, i just always smoke underneath my window so hopefully not too much smoke gets to the plants, i know touching your plants with fingers covered in baccy resin can give them tobacco mosaic virus, but i think if you just try to keep it to a min it shouldnt make much difference.