Most people mean "Windows machine" when they say "PC" though. Since the way people use a word define the meaning of the word more than even a dictionary definition, PC does in fact mean Windows machine.
I'd argue that "PC" has two meanings then. I'm going for "non-Mac PC", since that's what the title implies by separating Macs from the rest of PCs, and because I don't feel sensitive to exclude a huge set of possibilities.
It definitely has two meanings in the same way that "hacker" does and it is all contextual. If I hear hacker outside of this website I usually assume it is being used derogatorily.
In the "I'm a Mac, I'm a PC" context there is no confusion what PC means. In Hacker News context I can understand how the term PC might be ambiguous. I am really arguing that at this point though even hackers are calling Windows machines PC's. Although I have always wondered why everyone refers to them as PC's I have never found myself being confused when I hear it nor have I ever been misunderstood when using the term.
Exactly, that's why I assume everyone who is on Hacker News is aware of the Linux branch of operating systems, and at least isn't naive enough not to consider them in this kind of choice.
It's not the same. If you say "Mac or PC", it is understood that you mean "Apple computers, or other type of general-purpose personal computers, i.e., non-Mac PCs". But if we interpret "PC" only as "Windows computer", then there's this huge number of OSes we're not taking into account, since we're just considering OS X and Windows.
I suggest that we're all getting a little too pedantic here. The point is it's basically all the same hardware. You can buy anything and put any OS on it, although it's not so nice to put OS X on hardware that didn't come from Apple.