The first time I realized was during high school when I noticed one of my friends was wearing underwear suspiciously like the ones I had just changed out of when I got home from school. After he left, I checked my washing basket and my suspicions were confirmed. Suddenly everything that had been going on made sense. The underwear I put in my washing basket seemed to disappear, then reappear a day or two later. After that I took notice of what he was doing and discovered he was doing it every time he came over. That made me very curious, but it took me quite a while to find the courage to asked him about it.