I once got questionned when i was buying some SCISSORS, the assistant asked me for id but then backpedalled on realising how silly she was being, both due to the fact that I questionned why you needed ID to buy scissors, and the fact that she realised that, on second glance, i probably did look quite a bit over 18, so she just said "you're sure you're over 18 aren't you? you're not planning ondoing anything dangerous with them?"
er... well, no I thougth i was over 18 but i'm not quite sure now you mention it, but i definitely
am planning on going on a rampage and massacring people in the car park, but hey...