A man walks into a tee shirt store. 

There are three shirts on display.

 The first has a picture of Richard Nixon with a white mustache.
 Below the picture is "Got Milk."

 The second tee shirt has a picture of Ronald Reagan with a white mustache. 
Below the picture is "Forgot milk."

 The third tee shirt has a picture of Monica Lewinsky with a white mustache on
it. It is entitled "Not Milk."