As the title says... What was the dumbest mistake you ever made when playing Gal Civ?
This happened to me today. I was playing as the Drengin, and had just designed my 'Kona Class Mk2' ship. Except I mispelt the name. So I thought 'no problem, I haven't built any yet, I'll just upgrade the design'. So I did so, switched all my production to the new design, and went on my way.
A few turns later, and my grand armada is assembling on the Iconian border. Just as I am preparing to give the order to attack, I notice something strange. 0 attack in all categories. Is this a bug?
Nope. It's because when I upgraded the design to correct the spelling, I forgot that all the weapons and other stuff would be wiped... Needless to say, the underling responsible WAS exterminated.
Fortunately, I was already winning by miles, and I spotted the mistake just before the war started, but I came oh so close to sending a massive fleet of unarmed suicide ships as an assault force.