Quintilian Institutio Oratoria 6.3.25

[25] Further, things designed to raise a laugh may either be said or done. In the latter case laughter is sometimes caused by an act possessing a certain element of seriousness as well, as in the case of Marcus Caelius the praetor, who, when the consul Isauricus broke his curule chair, had another put in its place, the seat of which was made of leather thongs, by way of allusion to the story that the consul had once been scourged by his father: sometimes, again, it is aroused by an act which passes the grounds of decency, as in the case of Caelius' box, ¹ a jest which was not fit for an orator or any respectable man to make.