People may ask a "stupid" question mainly because either they have a lack of knowledge or you have an excessive amount of knowledge that you feel the question is "stupid." So in all, people really don't ask stupid questions they just ask questions that you feel are common sense. Or people might purposely ask a stupid question to be funny or annoying. Everything is relative. What's common knowledge where you are may not be somewhere else, and is most likely not stupid in the locale of the person asking.
Examples of so-called stupid questions :
Is it OK to use the AM radio after noon?
Why do they sterilize needles for lethal injections?
What is the opposite of medium?
They say that only one in four rapes are reported. How do they know?
Can we spell creativity however we want?
What does "new and improved" say about the old product?
Are eyebrows considered facial hair?
What do you do when you see an endangered animal that is eating an endangered plant?
If a guy that was about to die in the electric chair had a heart attack should they save him?
If an ambulance is on its way to save someone, and it runs someone over, does it stop to help them?
How old are you before it can be said you died of old age?
If it's zero degrees outside today and it's supposed to be twice as cold tomorrow, how cold is it going to be?
If you try to fail, and succeed, which have you done?
You know that little indestructible black box that's used on airplanes? Why can't they make the whole plane out of the same substance?
If you're driving at the speed of light and you turn on you headlights, what happens?
Why don’t you ever see the headline Psychic Wins Lottery?
When cheese gets its picture taken, what does it say?
If man evolved from monkeys and apes, why do we still have monkeys and apes?
Is it rude for a deaf person to talk (sign) with their mouth full of food?
What do you call a male ladybug?
If you can enjoy yourself, why can’t you enjoy anyone else?
If Pinocchio said, “My nose is about to grow”, what would happen?
If a deaf person has to go to court, is it still called a hearing?