Breaking the Flourite ( genuine Flourite not the Chinese `Flourite') element of my Vixen 70mm F8 Vixen Apo refractor one night. I had taken the screw on lens hood off to clean the front element and cross threaded the hood when trying to get it back on. Light bulb goes on and I grab a rubber ballet and give the hood a fairly benign tap to get it back on the correct thread.
Theres an immediate `chink' and I look in to see one element clean split in two. These optical tubes were about 4 weeks wages in 1985. All I could do was laugh as it felt a lot better than crying which was my only alternative