1. Humor can poke fun at foibles of others but should never
be designed to wound, abuse or offend
2. Quintilian: "The Gravity in which a jest is uttered
increases it attraction." (i.e., dry humor)
3. Quintilian: "As for obscenity, it should not merely
be banished from...language, but should not even be suggested." (Quintilian
even rejects the use of double entendres)
4. Cicero: Never use humor when attacking wickedness (crime) or
speaking about victims of great wretchedness
(poverty/hunger/sickness/warfare). "the things most easily
ridiculed are those which call for neither strong disgust nor the deepest
sympathy."
5. Try not to appear insolent or arrogant when using humor.