Probably my absolute favorite evidence against creation/intelligent design is the giraffe‘s laryngeal nerve. Put simply, it is a nerve which, in a giraffe, travels several meters in order to reach a destination mere centimeters from its starting point. This is due to the fact that evolution works with what it’s got; it cannot go back and fix things. An intelligent designer would have had the laryngeal nerve travel directly from point A to point B, but in every single mammal it instead travels down the neck, around the aorta, and back up the neck to the voice box.
Here’s a video of Richard Dawkins explaining exactly how the laryngeal nerve works in a giraffe: