The phrase "fin-de-siecle hubristic mania" is a combination of French and English which, roughly translated, means "End of the Century Over-Confident Insanity."

The term originated in the Ed Regis novel Great Mambo Chicken and the Transhuman Condition, and it described the seeming insanity offered by respectable scientists such as Eric Drexler, Marvin Minsky, and Hans Moravec.

Here we have these extremely digified, certified geniuses, scientists even, talking about machines that can manipulate atoms, computers that are smarter than man, and freezing people so that their potentially dead state can be fixed in the future! All of this ultratechnology, surely it must be mad delusions of deity-defying nature!

Quite obviously, Regis inteded for this phrase to be used with tongue in cheek.

In a sense, this expression, this mania, can be summed up very nicely by Arthur C. Clarke's First Law.