A curious minor feature of the defence of Plato’s character is Bessarion’s assertion that he was rarely seen to smile and never laughed (4.1.16). This is advanced as a proof of his modest and upright nature. The idea has precedents both in patristic and in pagan thought. The Greek and Latin fathers of the church had little use for laughter, Jerome being especially severe.10 A pagan parallel can be found in Porphyry’s portrayal of Pythagoras.11 There were Christians who believed the same to be true of Jesus. St John Chrysostom in one of his homilies on Matthew asserts that Jesus never laughed or smiled, giving as his reason the fact that none of the evangelists ever says that he did.12
source : Nigel Guy Wilson - From Byzantium to Italy_ Greek studies in the Italian Renaissance,p 60
possible bagage culturel ancien ?