Re: Which OS do you hate the most.
Windows NT 4.0 Server. The most rediculous OS ever. Here you installed IE 4.0, BSOD. SP2 installed, rebooted, BSOD. Connected with Hotswappable Compaq RAID, ran auto detection, BSOD. Installed Exchange 5.0 or instaleld on Xeon, same Sh!t. The Admins back then (some 7 years ago) would see BSOD more than the cup of coffee in a single working day. It worked well only on Alpha servers, but than application compatiblity. Man, I used to have nightmares of those memory dumps. 
I must say that XP and Windows 2003 are good products by MS. Despite of its vulnerablity for cracks.
In Unix, BSDs and Irix are quiet iritating. I didn’t like HP-UX in the beginning, but having work on it for last 4 years along with classic Solaris and bugger Aix, its more of a norm now. But Irix is still pain in the neck till date.
OpenVMS was also something which I never wanted to even type a command in. But was forced to learn it for Oracle and Rdb servers. Its one heck of a stable OS and its unhackable too 
So less work for security admin.