I've got nothing as catastrophic as those failures.  My blunders tend to be very subtle oversights that appear very minor and even insignificant at first, but eventually work out to be full-blown screw-ups.  Mind you, as far as kamikaze starbases go, I once wiped out three players full fleets with a single starbase.

I often tend to break out my support vessels (guardians, overseers, subverters) out of my fleet and use ctrl groups. Then after a battle is won I reform them into the fleet to jump. I do this because I hate all that 'reforming fleet' movement during battle which really wrecks subtle positioning.

Anyways, one time I had forgotten my overseers and subverters were split out and jumped the rest of my fleet into a heavily fortified gravity well. I had scouted ahead and managed to jump my fleet (sans overseers and subverters) around the ridiculous mining field choking the lane entrance and then start to engage a large fleet. Once I realized my overseers and subverters were accidentally left behind I blithely ordered them to jump and join my fleet in action.

Sadly I did not reckon that the path they would take would lead them right into the heart of the mine field. And since I was preoccupied with a large fleet battle already it took me a while before I noticed that I had lost more than half my support mini-fleet (something on the order of 15 overseers and an equal number subverters were lost outright). Many of what remained were heavily damaged but at least once I noticed the problem I was able to intervene and extricate them to the best of my ability. While I won the battle, I had lost a bunch of my support fleet. Very silly in hindsight.

That big red button... man.   it will get ya.  For me its like. YES! they are retreating! ohhh SHHIII-  RUN AWAY!  I have never lost a cap ship to one, and it as never cost me the game yet... but I have used it to great effect. its so fun watching a capital ship go from lv 1/2 to lv 6/7 instantly.