When I lived at home, it was like my mom knew but was in denial in one way but yet would buy me pot t shirts. My step dad busted me smoking in my room one day and all he did was say in a firm voice "I told you Not in the house" he then took my pipe and new bag of weed and I didn't hear anything about it till one day my mom brought it up and told our nanny in front of me hehehe My mom knew she couldn't tell me not to smoke cause I'd just say "Well you did" and well that would be end of conversation hehehe Also when I countered her reasons to not do it, the only one she could come up with to be valid was that it was illegal and I could get busted.

I'd tell em that you want to be stright up with them and not have to lie to them and tell em you like to smoke it. you get points for being honest but they may not like u doing it but wont come down on ya too hard. Just don't have any or pipes around at the time.
Be cool