[Weird] What is your useless knowledge?

I was talking with JD, Mirweis and Fab about the concept of useless knowledge: the specific knowledge in a targeted area every individual has. For instance: football players from 80s (Fab), merging companies (me), nuclear submarine (Emmanuel)... I can personaly draw a topic map of Napalm Death former members and their connection with various undeground music scenes (electro, doom,...).