Diplomacy can be many things.
Diplomacy can be, poise, politeness, delicacy, finesse, etc.
Diplomacy is being as nice to someone as you have to be.
Diplomacy can be politics, artfulness, and craft.
Diplomacy is making someone feel like you enjoy their company, while, deep down, you know that they are a gigantic PAIN IN THE ASS !
Diplomacy is not ignorance. On the contrary, most of the people to whom you have to show diplomacy are ignorant.
Diplomacy is not impoliteness, rudeness or bad manners. . . . BUT MOST IMPORTANT. . . .
Diplomacy is telling someone to GO TO HELL, after which they are very excited about making the trip.