That's called 'not spending time in the sun', heh. I rarely go outside when it's sunny because I hate the sun. So I get comments on my super white skin all the time
Actually I go out in the sun all the time and I can never seem to tan or burn. I have layed out in the sun for hours on end and sometimes end up falling asleep but, I never get any darker and I have never had a sun burn in my life. I had sun poisoning once when I was about 7 but, other than that...nothing. So its not because I don't spend time in the sun because I spend all my free time in the sun.
I used to tan easily when I was little, but now... not so much. Like you said, I can lay out in the sun or walk outside for hours and never get a shade darker. I rarely do that though because I hate the heat and I avoid the sun even more since I got sun poisoning a couple years ago. It was awful. Idiot that I am, thought I could go swimming from 1-4 in the afternoon without wearing any sunscreen. I couldn't wear a shirt for days. The entire top layer of my skin dried up and fell off (not your average peeling- I'm talking burn scabs and blister fluid) and I am just now
getting the original color back on my shoulders.
I've always disliked the sun (I used to stare at it when I was little and now I'm practically blind) but that burn is what pushed me over the edge. I'm like a mole now. My windows are always covered and I only willingly walk outside after the sun goes down.