Man i lied to my parents about it for a year. they found out anyway and were super-pissed about the lying, even more pissed than about me actually smoking. maybe if you tell them the truth about that you can convince them you dont do anything harder, even if you do i would deny that part.
You really shouldn't have lied man, cuz now if they catch you later, then you're fucked. but oh well, that's your shit to deal with, gald ya got through it without any punishment. congrats.
if your parents are soooo cool tell them the truth. they already know you smoke if you pulled out a nug in front of your sister, dont think they dont know about that now. admit you have done it but dont start spouting off how it should be legal and how much you love tommy chong. just admit to a modest amount of times you have "experimented" and point out the fact you arent a junkie, no need to bring up your parents past either, this is about you not them. also. dont smoke in the house, that may be what this is all about to begin with, respect. they might have smoked before but never in their parents home. instead of saying you will never smoke again if they press the issue, say they will never have to hear about you smoking weed again. just dont rub it in their face or get defensive.
my parents are no soooo cool, they WERE such potheads... now they're fucking accountants, lol. but if u read what happened i did admit to experimenting w/ weed, but nothing else. and my sister didn't tell my parents about me smoking with her. that'd incriminate her as well since she smoked it with me.