****Spoilers Possibly Below!!!****
****Proceed at your own risk****
For those that are saying Chigur doesn't kill without a reason and that the coin flips don't mean anything, I totally disagree. I think if it came up tails, that gas station attendant wouldn't have seen the sunset. And I think if the wife had made a call and it came up her way, she would have lived.
I don't think he's looking for a reason to kill...he wants to kill. It gives him pleasure. But I think the coin toss thing makes it more interesting for him...kind of like a gambling thing, where he's not only going to get off if he wins, but he's getting off on the game itself (which is how us true gamblers feel about it).
He's not looking for a reason
not to kill. He's digging the game. And he wants to kill...he lost at the gas station.