Just seen in a random channel on a random IRC server (with names randomly reassigned):
<Tom> http://onestepback.org/index.cgi/Tech/Mac/MyMacCantCount.red
<Dick> hm, reminds me of 4th year, one guy's computer kept getting the name of the weekday wrong
<Dick> turns out another 4th year had hacked in and changed the strings in his libc6 english locale file :)
<Harry> Man, I'm totally gonna do that to Joe
<Dick> yeah, it's a good trick... really hard to track down
<Dick> especially if it only happens on mondays :)
<Tom> I did that to Jack once
<Tom> early january a few (7) years ago
<Tom> I changed his locale, changing Monday to Mondak, January to Januark etc
<Tom> and set that as the system wide default
<Tom> that left him very confused
<Dick> I remember one guy had a directory full of sarah-michelle geller pictures, and changed his background every 15 minutes to a random picture...
<Dick> I managed to copy a photo of our lecturer into that directory
<Dick> and was lucky enough to be in the lab when it eventually was randomly chosen
<Harry> bwahahaha
<Tom> yeah we had some SMG fans around too
<Tom> although I didn't have write permission
<Tom> I remember writing a script that waited 5 minutes then changed someones background to solid black/white several times a second
<Tom> we also added xhost + to some peoples .xinitrc and would pop up xeyes on their machine
<Tom> or we'd ssh in and start a new X server running xlock so they'd come and sit down and discover we'd locked their machine
<Tom> we also had the second xserver connect to the citrix metaframe
<Tom> so they'd be typing away on their emacs and suddenly their machine would appear to be running windows and asking them to login
<Tom> good times