fooboy would be perfectly fine: a doghouse is not a dog. and the namespace for humans is much more "lexically bound" so we don't tend to get confused when multiple people are named John, just as we don't get confused with multiple cases of foo used as a metasyntactic variable; in fact, we expect it, unlike foobar2000 which demands exclusivity.

Does the "2000" in foobar2000 qualify it somehow? No. Do you make sure to say Windows NT 3.1 every time you mention it? no, you say only the qualifying part that makes your point: Windows, or NT, or 3.1 because the term is decomposable. fsckboy does not suggest "decompose me" other than etymologically suggesting "this guy uses unix; this guy doesn't use the gui; this guy is a wheel"

Economists use the term "widgets" in their examples. "Let's say a factory makes widgets, and the cost function is given by..." If you as a professor were to say "let's say a factory makes cars..." you would get responses from the class of "that doesn't make sense! cars blah blah blah" it's very convenient to use a variable that does not come freighted with meaning.

then there's the case of Little Bobby Tables...