Here is one that just came to mind; A guy tried to make me believe that a bullet from a rifle actually rises when it leaves the barrel. And he would have nothing of physics and science from me. So I asked him, "Then does that mean if you turn the gun on it's side and shoot it, the bullet will curve left or right?" He replies, "It still rises!" So then I asked, "How does the gun know when you are shooting it right side up?"
Yeeeessssssssss!!!!!!!!!!!!
The only thing that would make it any more awesome would be a fake can.
A friend of mine has a semi auto tommy gun. Took it to the range, fired a few rounds. A sheriff walks up and says he has one like that, but his is broken. when he pulls the bolt back, it locks in the open position. the only way to close it, is by holding the cocking lever, and pulling the trigger. once closed it won't fire.
DUH its open bolt!!!!
The often quoted law that you can't shoot across water.