I'd say my weirdest nickname is actually the one I use most now with my friends, Kiri. The name itself isn't weird, but the reasoning behind originally getting it was. I had a friend who was pretty quiet way back in middle school and early high school, they were a foreign exchange student from Japan, and one day, I forget the exact conversation, but they called me Kiri, which they said meant haze, and their explanation was just something along the lines of "Because you're so mysterious and you can disappear quickly"