My DH and I were fooling around back in high school , and he caught a glimpse of the stretch marks on my hips.  He touched them lightly and said, "Wow, cool.  Tiger stripes."  (He was 18).

I burst into tears and left his house.

Needless to say, we talked it over later, and he was befuddled at my reaction.  He'd never seen such a thing before and thought they were cute.