DUH I
From Reader's Digest

1) 
   When my wife and I worked at a Navy base in northern California, we received an invitation to an important dinner party given by the admiral. The date was the same day our first baby was due, so we sent our regrets. My wife telephoned the admiral's secretary to explain. "We would love to attend," she said, "but that's the day I am due to have a baby."
   "That's too bad," replied the secretary. "You know, I told him we should have mailed the invitations earlier."

2)
    Shopping at a supermarket for a last-minute party, I plopped a bag containing five tomatoes on the checkout counter. The cashier put the bag on the scale and started punching numbers. Then, to my surprise, she paused, took the tomatoes out of the bag and began weighing them individually.
   "Why don't you weigh them all at once?" I asked.
   "Don't be silly," she replied. "They're all different sizes.

3)
   When my husband and I arrived at an automobile dealership to pick up our car, we were told that the keys had been accidentally locked inside. We went to the service department and found a mechanic working feverishly to unlock the driver's -side door. As I watched from the passenger's side, I instinctively tried the door handle and discovered it was open. "Hey," I announced to the technician, "It's open!"
   "I know," answered the young man, "I already got that side."
 
4)
   As a salesman in a photographic supply store, I was demonstrating a telescope to a customer who had recently become interested in star-gazing. I pointed out that he could attach his camera to the telescope and take pictures of his celestial findings.
   "That sound great," he said, "but wouldn't I need a really big flash?"
   
Contributors:
1. Paul Cain
2. Daniel P. White III
3. Debby Mosely
4. Duncan Burnham