Tact

Tact is a prudence or a sense of politeness necessary in conversation with friends (or enemies) to maintain a good relationship.

Tact has similar meaning to diplomacy.

Examples of tactfulness are:

• not speaking at all, where there is nothing complimentary to be said
• saying something complimentary even if it is not apparently true (i.e. "That's a unique hat you are wearing."—a compliment though unique may be interpreted in many ways)

Examples of untactfulness are:

• stating that George Bush has big ears. (While possibly true it does not help improve the situation)
• any detrimental comments about a persons appearance, hygiene, or behavior