This may come as a shock to some, but one word can sometimes have multiple meanings depending on context.

"Evolution is just a theory."

If I hear that one more time I am going to scream.

Yes, evolution is a theory. But--hear me out--that's a good thing.

People who use this (very weak) argument are misusing the word 'theory'. They are using it in its colloquial sense, not in its scientific sense. There is a HUGE difference there.

Colloquially, a theory is a guess. In science, we call that... a guess.

Slightly stronger than a guess is a hypothesis. One arrives at a hypothesis after making some preliminary observations on the object of study, and using these observations to make a more educated 'guess' at what is going on. After a hypothesis is formed, one creates an objective experiment to verify or debunk the hypothesis.

Once enough information has been collected, and the experiment has proven to be repeatable (that is, anyone else could do the same experiment and get the same result), then the idea may be approaching the level of theory. A theory must be shown to be consistent, and, what's more, it must have considerable predicting power.

This is the key difference. Colloquially a theory is a haphazard guess about the cause of something. Scientifically, a theory is an explanation of something that is consistent, objectively verifiable, and can be used to predict future events. A scientific theory is a very strong statement.

If you're going to cover your eyes and refuse to see the evidence provided for something, that's one thing. You have every right to refuse to believe what we can see and instead believe something with no evidence for it. But if you're going to try to debunk this evidence, do it scientifically, not semantically. Learn about what you're arguing against, and who knows, maybe you'll find some key flaw in evolution, something that blows the whole thing out of the water.

And if you do? That's great! We'll find a better explanation! That's the beauty of science--if something is shown to be inconsistent or 'untrue', we'll throw it out and find something better.

But of course, that'll be "just a theory" too.