Ah, good times. Our lab ran sshd on each workstation, so I launched cli processes on every system, at daytime, with dozens of students still working on their project. I thought running as "nice -n 19" would be safe.

Wrong. My program ran out of memory, systems started thrashing, desktops froze up. Confused students, panicking about unsaved changes, swearing, rebooting. Meanwhile I was frantically trying to kill my processes, but even sshd became unresponsive so I couldn't stop the madness. They never found out it was me :)