That term existed well before SpaceX - From Bureau of Naval Personnel, 1970 - Fire control (Naval gunnery) https://books.google.com/books?id=86zpYQO5yYcC&q=Rapi

That term existed well before SpaceX - From Bureau of Naval Personnel, 1970 - Fire control (Naval gunnery) https://books.google.com/books?id=86zpYQO5yYcC&q=Rapid%20unintentional%20Disassembly&dq=Rapid%20unintentional%20Disassembly&hl=en&sa=X&ved=0CC0Q6AEwAjgKahUKEwisiKjUh_TGAhWIGx4KHYQCC-o#v=snippet&q=Rapid%20unintentional%20Disassembly&f=false https://books.google.com/books?id=86zpYQO5yYcC&q=Rapid%20uni... and https://history.nasa.gov/monograph45.pdf https://history.nasa.gov/monograph45.pdf > We would build multiple layers of fuel oxidizer, and then, we would get a run long enough up to really do something. We’d get a really exciting event. I deemed it “pre-unplanned disassembly” at the time. That problem really went away when we learned a little bit about fuel control and kept injectors and propellant temperatures a little warmer.