It feels like to ME, your dads having issues of a different kind, seperate from you alltogether. i seriously doubt that you smokin weed is on the top of his list of stresses. if he smokes he probably does so FOR stress relief and such...a better angle MIGHT be to ask him whats on his mind. or whats troubling him...and as you do it, pass that dutchie! (always to the left hand side ;P) assure him its yours and not his, and that if hed like..you two can sit and chill and talk things thru. its not hard, its just tension, like you said. well we are ALL 'tense' HERE..lol relieve him of stress and youll be amazed at the changes made.