We'll give him more than chains. He's always been King of his world. But we'll teach him fear! We're millionaires, boys, I'll share it with all of you. Why, in a few months, it'll be up in lights on Broadway: 'Kong - the Eighth Wonder of the World!'
"Eighth Wonder of the World" was the working title of a screenplay started by David O. Selznick in the early 1930s, which later developed into the classic film King Kong.

The use of this phrase in King Kong illustrates what it really is -- a stock phrase used to hype a spectacle for profit, by attempting to invoke Herodotus' Seven Wonders of the Ancient World.

Although a few may naively use this phrase to describe their favorite thing in the world, most users are humbugs out to make a profit. Whenever you hear this phrase, hold on to your wallet; if you really must go see, bring along a block of salt large enough to sit upon, and prepare to be disappointed. And don't bring back any Feejee Mermaids!

A quick Google search finds the following things saddled with the unfortunate moniker of "Eighth Wonder of the World":

You get the picture; I'm not going to go through all 143,000 entries. I needn't go into peoples' descriptions of the anatomy of their significant others.

That's not to say that some of these things aren't wonderful to behold, and worth parting with some of your hard-earned cash for. However, I do wish their promoters had been more original and not used this tired old phrase. It's usually hyperbolic, and always subjective, a way of indirectly saying