"Let me tell you about my life"

Every parent has a different challenge with their kid. My current one is that I cannot get my 7 year old son to stop talking. You would think that this is a problem with girls, but my son can out talk them any day! Yesterday I took him to the nurse for a mandatory skin test required for school enrollment. By the time he walked out of the clinic, no less than 10 people knew that he had taken the test and the procedure involved. Then we stopped by to buy an antenna at Radioshack - by the time we walked out (in 5 minutes), the cashier knew that he had 41 dollars in savings - 2 $20 notes and a dollar note. He also had a fake million dollar note but he knows its fake. People seem entertained by his behaviour but I'm confused. How do I curb his need to pass data to everyone he meets? I think my son is needier than most - for attention - he wants to be the clown in the crowd - he wants people to like him and laugh at his jokes. But he does not handle a negative reaction well. Or worse, indifference! I need to make him realize his self worth, but I don't know how, as of now.