It's How You Ask

Corporal Conroy needed to use a pay phone, but needed change
for a dollar. He saw Private Duncan mopping the base's corridor
floors and asked him: "Soldier, do you have change for a
dollar?"

Private Duncan replied: "Sure."

The Corporal turned red, and said: "That's no way to address a
superior office! Now let's try it again. "Private, do you have
change for a dollar?'"

Private Duncan turned to him and replied: "No, SIR!"