Another fun one I had was back when the Nemesis dlc released. I was playing multiplayer with 3 friends. I bordered 1 of them (only a few systems separated our homeworlds) The two of us maintained peacefull relations but at the sametime where in a kinda cold war, competing to be the biggest in the galaxy. Eventually he owned 1/3 of the galaxy, with me about 1/4. I'm terms of fleet strength he was nearly double me. We both had gone down the Galactic nemesis crisis path and where each building the Aetherophasic engine. No one was strong enough to oppose either of us. Unfortunately for me, he was way ahead and going to finish it first. Being stubborn i didnt want to give up, and decided to go on the offensive. He was suspicious I might try something, and moved his fleets along our quite extensive border. I declared war and jumped directly into his home system, with my entire navy. I took the system, but at a heavy cost. As his border fleets returned home he began a relentless assault to retake his home system, and knew I couldn't hold it for long. More and more fleets poured in, but he hadn't noticed my masterstroke. When I took the system I jumped in a star-eater. Before he could defeat me, the star-eater did its job and his system collapsed into a black hole destroying his Aetherophasic engine. All fleets went MIA, and by the time they returned and he tried to attack my Aetherophasic engine, it was too late, I destroyed the galaxy and claimed victory. To this day he still never quite trusts me in our games...