One single proof

Scientists are trained to overcome a one-shot, "cowboy" mentality. When great scientific ideas do fall, on rare occasions, they do so of many grievous wounds followed by the rethinking of the total picture. The idea, literally worshiped in creationist circles, that you can disprove a theory by whipping out some cute, isolated "proof" that settles everything at once and for all, is not scientific. "One single proof" is a deceptive rhetorical flourish used primarily by denialists designed to apparently negate a preponderance of circumstantial evidence by claiming that without a specific key proof, the whole argument is invalid. The effectiveness of the technique is dependent on a sort of distortion of Occam's razor whereby any evidence that does not provide the whole answer is ignored.

The fallacy often rests on the idea that without a particular key bit of information, the entire system will fall apart. While this is sometimes the case, particularly when dealing with mathematical proofs, forensic arguments often make use of large quantities of circumstantial evidence in such a way as to point directly to a cause without a single smoking gun.

It relies on the idea that certain proofs would be sufficient to prove an argument but are not necessary. As such, it is an example of denying the antecedent.

Examples

 * In Holocaust denial, the insistence that the history defender produce a written order from Adolf Hitler ordering the extermination of the Jews, despite the fact that Hitler's desire to eliminate Jewry was fairly well-known without an explicit order being issued. They have also requested an autopsy report of a Jewish prisoner proved to have died from gassing.
 * Creationists often demand "one single transitional fossil", usually according to their creationist definition of the term (ie, one not recognized in scientific circles, such as a fish turning into a monkey or a dog into a cat).
 * Among tax protesters in the United States, demanding that the government show the protesters the law authorizing the income tax, while denying that the 16th Amendment to the Constitution (which they claim was never properly ratified) and Title 26 (the Federal tax code) constitute sufficient authorization in the eyes of the US Federal courts.
 * Among deniers of the harmful effects of tobacco smoking (active and passive), demanding that public health authorities produce the death certificate of one person who died as a consequence of exposure to secondhand smoke, and, in the absence of such a death certificate, concluding that such exposure is innocuous.
 * Global warming deniers will sometimes ask for "one single study" that shows CO2 is a pollutant (which is in not even wrong territory). Another angle, as Roy Spencer takes, is to ask this: "Show me one peer-reviewed paper that has ruled out natural, internal climate cycles as the cause of most of the recent warming in the thermometer record."
 * Flat Earth believers sometimes ask for a measurement unambiguously "showing the curve" of 8 inches per mile, ignoring that the Earth's surface is irregular and not a perfect sphere. They also ask for "real pictures of a spinning ball from space" only to blindly reject them once such image is delivered.
 * Anti-vaxxers sometimes ask for a specific study that compares groups of vaccinated people and non-vaccinated people to see which one is healthier. Of course, they never consider the fact that demographic differences between vaccinated and unvaccinated populations means such a study would never produce any reliable results.
 * COVID-19 deniers often ask for one healthy person who died of COVID-19 and not a comorbidity.