Moderatio

Quatenus autem sint ridicula tractanda oratori, perquam diligenter videndum est, id quod in quarto loco quaerendi posueramus. nam nec insignis improbitas, et scelere iuncta, nec rursus miseria insignis agitata ridetur: facinorosos enim maiore quadam vi quam ridiculi vulnerari volunt; miseros illudi nolunt nisi se forte iactant. parcendum est autem maxime caritati hominum, ne temere in eos dicas qui diliguntur. haec igitur adhibenda est primum in iocando moderatio.
(Cicero, De Oratore 2.237-238)

But the limits within which things laughable are to be handled by the orator, that fourth question we put to ourselves, is one calling for most careful consideration. For neither outstanding wickedness, such as involves crime, nor, on the other hand, outstanding wretchedness is assailed by ridicule, for the public would have the villainous hurt by a weapon rather more formidable than ridicule; while they dislike mockery of the wretched, except perhaps if these bear themselves arrogantly. And you must be especially tender of popular esteem, so that you do not inconsiderately speak ill of the well-beloved. Such then is the restraint that, above all else, must be practised in jesting. (tr. Edward William Sutton)