Crop circles are a real, proven, phenomena that nobody has been able to replicate, or explain. In the 1990s in the UK - where most of the activity was happening, it got to such a fever pitch of wanting an explanation that a major news company did a live broadcast in order to capture a UFO creating a crop-circle. Some military and governmental fuckery later, the guy who predicted it was going to happen was moved to another field by order of the army. He filmed a field he knew wasn't going to capture the ufo on film, and he didn't. However, the original field he was filming was hit with a crop circle.
Following this, two random people came forward saying they made the circles with sticks and string, despite the fact their circles were basic in geometry, tore the corn - unlike a UFO crop circle, and the men couldn't possibly travel the distances they said they were, while making a circle, unseen, in the night. They even went to France to create a crop circle, then came back to the UK the following night to make another. They did this as a prank, apparently. (It's all bullshit and there's a good Why Files episode on this).