Rebecca - a flying start
This has to be one of the best Monday mea culpas to date: a protagonist who is absolutely to blame and in circumstances I (and I expect many of us) can identify with. Did Simon leave you this story lined up, or are you just better at it?
I'm sure the only reason I've never done similar is that I've never been in charge of a mainframe. Though it brings to mind a few 1980s-vintage pranks, from when Unix machines trusted each other and would happily share screens (xhost + was a default setting). Or the one on VMS that had the company go into panic mode for a major security breach 'cos I altered my logout to display a logout screen for "SYSTEM".
Here's a thought. These days when bored like that, one can turn to the 'net and browse something - like the day's crop of Reg stories. I wonder if that's substantially reduced the rate of "bored" pranks, and accidents like this?