PDP 11/44 (running RSX/11 IIRC) at uni shared between a dozen postgrads (including me), who needed superuser privilege to use the video hardware. One who had several accounts wanted to remove all his old files so lazily typed rm [*.*]*.*;* instead of removing one UID at a time. Everything including everyone else's files and the OS (and all system utilities) disappeared, and of course the last backup was months old. Of course the files were still physically there but no longer accessible.
Luckily I'd been running the system debugger and it was still resident in memory (all 64k of it...) as was the printer driver, so I managed to print out the block allocation of the (20MB) hard drive on the line printer. Said user then had to use the debugger to manually reallocate every block on the disk by hand one at a time to the correct UID (including the OS) and filename. Took him all weekend...
[no it wasn't me, but I was the defacto sysadmin when people suddenly found they hadn't got any files any more]
Biting the hand that feeds IT
