1.their shoes.
2.how they act when they are dating/in love{eh, whole other post "the couple"}.
3.how they act in the water/at an amusement park.
4.what music they listen to.
basically you know the person inside out when you know these things. however, i added one more to the list while i was looking at my bulletin board a few days ago:
5.whats on their bulletin board.
here's me: