False. Theories cannot be proved. They can be supported or, in some cases, disproved.
The problem is that creationists do not bring scientific evidence to the discussion; they bring religious belief couched in scientific terms. A challenge to a scientific theory must first of all be based on science. If you go to Answers in Genesis or some of the other creationist websites, the level of science they present in most of their arguments would result in a failing grade in first year classes.
When someone DOES challenge, instead of responding like the mature adults that degrees in science might suggest them to be, they instead act like spoiled five-year olds who are told that Santa Claus doesn't exist.
Sorry, that is generally not the case. What you may be seeing is a natural reaction to the hundredth (or thousandth) time a scientist responds to a creationist's claim that the Second Law of Thermodynamics prohibits evolution, or asks "If we descended from monkeys, why are there still monkeys?" Even scientists do not have endless patience.
However, many who stump for evolution treat the subject as if it were proven beyond the shadow of any doubt. In fact, I've noticed that, when it is pointed out that evolution is a theory, meaning it is not proven and thus open for inquiry and scepticism (as with anything else in science), that they get themselves all in a huff about how creationists "just don't understand what science means by the word 'theory'", and the implied meaning seems to be that evolution is beyond the pale of investigation (and thus "proven").