Not a major disaster by any means but my worst ever one was about 30 years ago when I was in my teens.
I was fishing a lake near where I lived that had a few carp in it - a bit of a rarity in those days.
It was a day ticket only water and every Saturday night I'd been getting up at about 3.30am to walk the 4 miles to fish it and blank from sunrise to sunset.
One day I eventually managed to get one to take my boiled potato (out of a tin) bait. My fairy liquid bottle top indicator pulled up to the butt and line started to peel off from the open bail arm. AT LAST I thought to myself.
Played the fish on my "broom handle "for about 7/8 minutes and got it right into the edge where I could see it was a good size - would have been my first double and a very, very good fish for the period and the lake in question.
Bent down to pick net up, rod tip lifted, mouth came out of water, hook pulled and I was left watching it swim away.
I was absolutely gutted and sat there for about an hour in disbelief, couldn't even make the effort to cast out again.
To make it worse my mate turned up about 5 minutes later to see how I was getting on. if only he'd cycled a bit quicker...