I really can't believe there's anyone aged 18 or over (or even 17 tbh) who actually give a toss what their folks think. For God's sake, man up.
To be fair, I always ran everything by my folks when I was younger (and still do really) but they know I'm old enough (and have been since late teens) to make my own decisions. I think they just see it as their job to make sure I've thought it through properly first.
I know when I went to my first live, Mum made lots of comments like "Hmmmm, well, I suppose it'll be ok... won't it?". I think she was actually more worried that I was going to be camping by myself. Not sure why, I first went camping when I was just weeks old, and actually lived in a tent for 6 months...
But yeah, just to reiterate my point... If you're old enough to be legally responsible for yourself, tell your rents to poke it. On the other hand, if you're younger, you just need to learn to be more pursuasive.