I'd say mine was when I launched my first nuke(s). I was originally only going to attack Japan. So, I launched one of my 30 or so ICBMs and then the Aztecs declared war on me. So I launched some nukes on them, and on and on it went. Until I had gotten every civ mad at me, and I used all my nukes. Needless to say the AI's were hurt very badly, and they were all on diferent continents. So I finished up my last component for my Spaceship about 3 turns later. And I went ahead and launched it so I could leave all the nuclear winter I had just created behind (not to mention all the civs who hated me for turning about 25% of their land to desert, and creating MASSIVE Global Warming) Man, for a blunder I think that ended up working out good for me.