No, you're getting it wrong. There's a fundamental difference between a scientific theory and what the word 'theory' means in common parlance. As far as science is concerned, theories are fact. I'm too tired to explain all this, but read wikipedia and other reliable resources like talk.origins, and you'll understand.
Of course, there are always people who disagree with mainstream science, with theories that have gone nominally unchallenged for decades or even centuries. When dealing with these kinds of people, a certain level of discretion is advised. Some of them even might be scientists, but most of them will be not. Almost all of them will be crackpots. Or creationists, when discussing certain topics, but the difference is minimal. Even more of them will be wrong.
Actually, most of mainstream science these days is just.. right. It might not be complete, but it works. No matter how you look at it, it's good for what it's intended to be.