Loon Out Posted in L Best definition Loon Out To lose your fuckin mind. Simply put, whooping ass. This person kept calling my house, asking for someone who wasn’t there. I told them the next time they call I’m going to loon out on they asses. How satisfied are you with the definition? Looking for Loon Out meaning? Delighted that you discovered the greatest determine on our web site! Recently this definition was actually observed 116 times.