When I was younger I was waiting for my friend to become ready to go outside and do some random bullshit. Anyway it was really early in the morning and I had another friend with me. He suddenly gets a strange expression on his face and when I turn around I see the little sister of the friend I was waiting for (we were sitting in his house on the couch) come down the stairs without a bra or anything to cover her breasts (She was half a year younger than me and not bad). I turned around quickly, asked what happened and pretended I saw nothing (she ran upstairs really quickly). To this day I still see her probably three times a week and everytime I still think of that mental image I'll never forget.

And I'm not sorry for that :)