Here's a load. Some are better than others:
You know those "Keep Off The Grass" signs you sometimes see in the middle of lawns? How do they get there in the first place if you are not allowed on the grass?
Why does talking to God in a church makes you religious, but talking to God in the street makes you crazy?
If you spend all day doing nothing, how do you know when you have finished?
If you were on a plane going the speed of sound and walked from the back of the plane to the front, would you be walking faster than the speed of sound?
If man evolved from monkey and apes, why do we still have monkeys and apes? Why didn't they evolve too?
If swimming is such good exercise, why are whales fat?
Can you breathe through your nose and mouth at the same time?
Do octopuses have arms or legs?
Who was the first person to see a cow, and think what would happen if I pulled those dangling bits and drink the liquid that comes out?
If a cat always lands on its feet and buttered bread always lands butter side down, what would happen if you tied buttered bread on top of a cat?
Why does your nose run and your feet smell?
Why isn't phonetic spelled the way it sounds?
If you stole a pen from a bank then would it still be considered a bank robbery?
Why is it called pineapple, when there's neither pine or apple in it?
If you have x-ray vision, and you can see through anything, wouldn't you see through everything and actually see nothing?
Why is it you're 'in' a film, but you're 'on TV'?
Can someone give up lent for lent?