What is wrong with the general public’s line of thinking regarding theories

As a scientist I am often irked when non-scientists say “That’s JUST a theory!”. I get aggravated because the average person’s definition of “theory” does not match the scientific definition of “theory.”What is wrong with the general public’s line of thinking regarding theories? In other words what is a proper definition of the term theory?What is a word that might be a better choice for the general public to use here instead of the word “theory”?