To back this up, they will use such arguments as the Kalam Cosmological Argument, or The Fine-Tuning Argument.
However, what they don't realise is that if there is a God that wants to take credit for this universe, he must be incredibly inefficient!
Otherwise, the best explanation that fits the available data is that the observable universe started expanding from an infinitesimally-dense point roughly 14 billion years ago, and that life arose on earth by natural processes.
You walk in to a warehouse that is, for whatever reason, full of mattresses randomly scattered everywhere and you are looking for a place to sleep.
However, you find that this whole entire warehouse is a vacuum filled with radiation (so you can't breathe) and that the only mattress suitable for sleeping on is the size of a proton.
[Think about that: not even the size of a speck of dust - the size of a proton that makes up an atom that makes up a molecule that makes up a speck of dust]
Yet this is what the earth is in comparison to the rest of the universe - a small, insignificant ball (Jupiter alone is 317 times the mass of earth), being pulled by gravity, inside an inconceivably vast radiation-filled vacuum, being bombarded by flying rocks that have been know to trigger cataclysmic events.
So with this hypothetical warehouse scenario, if you walked in and noticed that the whole place was filled with lethal radiation and you couldn't breathe, you wouldn't suddenly conclude that that warehouse was designed for sleeping in (despite the abundance of mattresses everywhere) or that the warehouse was designed with one proton in mind.
When we look at a thing that exists, how do we infer what the function of that thing is? By what it does most often and most efficiently.
The heart's function is to pump blood, because that is the function that it does the most and efficiently at that. We wouldn't say that the heart's function is to cause heart attacks.
Doors function to open and close and give access to otherwise closed-off areas. We wouldn't say the function of a door is hit people in the face.
So let's look at this universe. What does this universe do most often and most efficiently? Collide galaxies in to one another, spread radiation everywhere, create new celestial bodies out of the scraps of old celestial bodies, and in extreme circumstances, create an object so dense that neither time nor light can escape, and the laws of nature as we know them get twisted right around.
How many black holes have we observed? Dozens.
How many intergalactic collisions have we observed? Approximately 100.
How many planets are there that have sentient and intelligent life on them? One. And only one.
So by that count, we can only rightly conclude that this universe was designed for galactic collisions and explosions, spreading radiation everywhere and for twisting the laws under certain conditions.
We could not possibly conclude that this universe was designed for human life.
Something to think about next time your Creationist friends start talking about the intelligent design of the universe.