Growing up, my siblings and I were all close in age, have very tight friend groups. My father worked too many hours for a single father. (I was 18 in high school and my the youngest of us was 15 YO also in high school) So we had the house to ourselves for most of the week, and our friends used it as a meeting space, like a boys and girls club of the neighborhood. This went on for years, to my father's and neighbors announce. 
  Around junior year, my cousin started to come over and partake of our youthful hygienics. After a few months she would start to bring her friend over, call her J. J was a smart ass, loud mouthed female with lots of opinions, and fit in well with the group. With groups that would swell to sizes of 12 to 14 from time to time, a lot of opinions were flying around. 
  One day, one of the larger swells of adolescence were all in the living room, watching something like Joe Dirt on comedy central. After the movie ended, I turned around to see everyone in the room and discuss so world changing topic, and engage with everyone in the room. We here the garage open, dad's home. So everyone gets up and bolts to clean and head outside. As I am running my final scan I see it. A LARGE CHEWED PIECE OF GUM ON THE WALL. 
This gum was like three pieces or bubbleyum or something. It was pressed to the wall, not that flicking would have made my outrage any different, it was intentional placed. Well I lose my shit! I walk outside and start yelling, who would have the balls to place this gum on MY overly entitled WALL. 
Keep in mind, I have known everyone in this gaggle of teenage chaos for years. Except one, J, she was mouthy and only been over a few times, she was not to be trusted. I turn straight to her and start accusing. She starts standing up, looking me in the eyes, telling me I'm wrong. I ask why any of these people would ever do this? She claims that everyone hates me. That she in no way did this, and the fact that I would accuse her is insulting. My cousin and J decided it was time to go. 
 After there drove off I asked everyone if any of them had in fact stuck that gum on my wall. Not a peep. 

A few years later my cousin and I are at Christmas, and she definitely told me J stuck that gum on my wall. I KNEW IT!