1. Any mindless jerks that don't correctly account for possible spaces in variable expansions when building commands to be executed. This mostly applies to shell scripts and makefiles. And it especially holds on Windows, where the default home directory path has spaces in it (at least through XP). And it seems to be very often violated on Windows, to the extent that people get the strange idea that environment variables like PATH should contain quotes around paths with spaces (it should be obvious why this is wrong to anyone that's spent much time with shell and batch scripts).
2. The mindless jerks that keep perpetuating the Win32 API's 260-character path name limit. There are some ways around it, but they don't help people using Visual Studio, which was developed by mindless jerks that adhere to the limit. Such a short limit would suck on Unix, but it sucks doubly on, say, WinXP, where new VS projects are created in a directory looking something like C:\Documents and Settings\aldimond\My Documents\Visual Studio 20xx\Projects. You're already 75 characters in the hole, plus whatever you need for the solution and project directories; if you have verbose naming conventions you don't need to go many levels deep from there to get over 260 characters. I usually keep my sources in $HOME/src, as I would on Unix, but with some of the projects I use at work I have to cut path names down even further. There are tricks you can use if you're really repulsed by having your dev files live outside your home directory (as you should be); most people just put them straight under the C drive. Which means that the 260-character limit perpetuates people's unwillingness to run as unprivileged users on Windows, one of its significant real-world security weaknesses.
3. The mindless jerks behind blogger.com, who don't have an option to require moderation on comments with links. As it stands I have to either subject honest commenters to moderation (which I don't want to do) or manually delete all spam comments (which is tedious and slow).