You are 10 - getting dressed for a school social - what are you wearing?
I often got the brief really wrong as a child because I loved clothes but I didn't really grasp what was "normal" to wear. In this case, I wore my mum's bottle green velvet ball dress, complete with an up-do and ringlets, and a choker with a bow on it and brown lipstick. I arrived and was literally the only one who had dressed like that - everyone else wore clothes that were very cool at the time - lime green or tartan miniskirts, knee-high socks, halter-neck tank tops, etc. Absolutely mortifying.
What second-hand item of clothing was your biggest score?
There have been so many. Shopping at op shops was such a massive part of my learning as a teenager - really it was so valuable to spend $8 on four different blouses that I could study the collars of - how they were constructed, the proportion to the rest of the garment, how changing the angle of the collar point changed the entire feeling of the garment.