On the street, I ...

In my flier I advertise that I do 2,000 sit-ups a day. Yesterday, on the street  a man about sixty dressed in a fine suit asked me to prove it. 
I lifted up my polo shirt to show him my flat stomach. He stood there for about a minute gazing at my stomach. 
I proved my point but it must have looked like I was showing him my..... 

You understand ....

Tim