Male ulciscitur dedecus sibi illatum, qui amputat nasum suum.
He who cuts off his nose takes poor revenge for a shame inflicted on him.
De Hierosolymitana peregrinatione acceleranda (1189), cited from Mary Beth Rose (ed.) Women in the Middle Ages and Renaissance (Syracuse, NY: Syracuse University Press, 1986) p. 29; translation from John Simpson The Concise Oxford Dictionary of Proverbs (Oxford: Oxford University Press, 1993) p. 55.
A similar proverb, Qui son nez cope deshonore son vis, appears in the late 12th century chanson de geste Garin le Loheren, line 2877.