Doctor of Philosophy? -- that's the canonical meaning. Permanent Head Damage? -- that's a good one. But the one I came across many months ago and believe that it is very interesting is this quotation from Rondam Ramblings' "Top ten geek business myths".
The only thing a Ph.D. means is that you're not a moron, and you're willing to put up with the bullshit it takes to slog your way through a Ph.D. program somewhere.
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I don't have a Ph.D. yet but I believe that I am not a moron, though. Hence, getting a Ph.D. will benefit me only the second phrase :D.