commentary: does expertise make you an expert?

In a (supposedly private) note to me, Chris T commented:

I remember reading [the expert/expertise post] and thinking "note to self: don't claim to be an expert on resume." You didn't really come to a conclusion, but the arguments you made against claiming to be an expert seemed stronger than those for.

I've always been intrigued by "being an expert." If you think about it, everyone's an expert, however temorarily, in some subject, however small.

For example, presently I'm probably the world's foremost expert on Value Level Metadata in the FDAs Case Report Tabulation format, if only because that's the page of the spec that is presently open on my desk. Ten minutes from now, I'll have relinquished the title, but then I'll have moved on to being "the world's foremost expert in how much coffee is left in the 3rd floor kitchen of B-----'s Montville 200 building." I have an ecclectic field of expertise.

It's all about the scope of your subject.