When I was smaller, my cousin told me to come outside because she had something to show me. At the time, she had on underwear and a skirt, She must have been about 13 and I was about 11. I followed her outside and we walked into the woods, she squatted down, showed me her underwear by lifting her skirt, then peed in her panties. I remember being so jealous that I could not do the same at the moment, if I had to pee right then, I would have done the same in front of her.
As a result, for the next few summers, because we were sort of out in the country a little ways, I would pee in my panties