> The 2 different OR’s mean many different things qualify as ostentatious as lone as 1 or more of the following applies. [...] The “often by” means it isn’t required for the definition to apply.
Read in such a decontextualized, selective, and uncharitable manner renders the definition worthless. For example, is any attempt to attract attention ostentatious? Any attempt to attract envy? Admiration? I think not. So your reading is inadequate and defective. Something is presupposed by the definition for it to make sense, which is to be expected, as dictionaries are not compendia of mathematical formulas written in some rigorously formalized language defined in the preface.
The first part of the definition does indeed use the word "often" which appears to soften the relation between gaudiness and the rest, but it still establishes a generality, i.e., that gaudiness is a reliable mark of ostentation. Otherwise, what's the point of including that in the definition if it isn't somehow characteristic of ostentation? It would not be a matter of definition, just an incidental thing that may or may not be true.
Note also the second part of the definition: "overly elaborate or conspicuous". Something that is overly elaborate conspicuous has transgressed some norm, has it not? Otherwise, how can you judge that something is "overly" elaborate? And if beauty is what satisfies a norm, then departure from the norm, either by defect or excess, is a deviation and so the thing in question has moved away from beauty toward ugliness. The technique used may be refined, but the composition can still be ugly. (And note that I, too, used an "or" in "The key to ostentation is vulgarity or crudeness, ugliness". I didn't think it needed to be spelled out.)
Now take the Oxford Dictionary's definition, which is arguably a bit sharper in this regard:
pretentious and vulgar display, especially of wealth and luxury, intended to impress or attract notice.
This definition leaves no doubt about the relation of vulgarity and pretentiousness to ostentation.
> A peacock display generally described as ostentatious but nobody calls it tacky.
Yes, people can use it that way, but this is an analogical use of the term. But the use of "ostentatious" in your original post was not this meaning, at least not according to a normal reading given the sum of all context clues. In fact, you wrote:
> I think Klimt is the only artist to successfully incorporate gold into his paintings without making them look obnoxious or ostentatious.
Wait a minute! Klimt's use of gold could be heavy by any standard. Most iconography, and most art that uses gold, in fact, doesn't lean into gold as much as Klimt does in some of his works. So something doesn't add up here. The only way you could make that claim is if the aim of Klimt's work, its form, makes legitimate such heavy use of gold. Furthermore, you say "obnoxious and ostentatious". Not pejorative? Could have fooled me! Is some defect, something vulgar OR crude OR ugly being suggested? How could something beautiful be obnoxious?