What's wrong with the dismissive "It's just a theory." reasoning?

How can you explain to the lay person the difference between theory meaning “my hunch” and theory meaning tested, found to be predictive, published and peer reviewed, tested multiple times by many others around the world, found to be predictive of other facts by others around the world, and thus confirmed to 5-sigma certainty?

If someone thinks scientific theory and theory meaning hunch are synonymous, then any “theory” anyone dreams up is as good as any scientific theory. That would make a hunch that bigfoot really exists or that we will someday discover Atlantis just as valid as the Theory of Relativity. The people who still believe in a flat Earth would be just as likely to be right as those who insist it is ball shaped. Geocentrism would have equal standing with heliocentrism.

What’s wrong with that picture? What’s the most effective way to help those unschooled in science understand the differences in individual hunch-style theory, scientific hypothesis, scientific theory and scientific law?