I've annoyed several people by my refusal to help their Windows problems. They usually shut up when I point out I refuse to even be paid for it, but they still don't understand it.

At work, we acquired a server from an external party for part of our application. The existing app is PHP and Java, sitting on Linux. This box is .NET on a Windows box. Their developers had trouble understanding that we had no interest in its internals.

Wade.