This is an old one but I don't see it here.
A man stepped out of his tent with his rifle and walked 1 mile south, 1 mile east and 1 Mile north. Then he shot a bear in front of his tent.
What color was the bear?
There are two places in the world you could be to be able to walk 1 mile south, 1 mile east then 1 mile north and end up where you started (in front of your tent). One spot is right smack dab on the north pole. The other spot (or infinite number of spots) would be just north of the south pole (about 1.159 miles) such that walking one mile south of camp puts you in a spot where walking east 1 mile puts you on a circle that ends where it started. There are no bears at the south pole, so that can be ruled out.