Avoid Speaking of Persons
Lose no time in setting before you a certain stamp of character and behaviour to observe both when by yourself and in company with others. Let silence be your general rule; or say only what is necessary and in few words. We shall, however, when occasion demands, enter into discourse sparingly, avoiding such common topics as gladiators, horse-races, athletes; and the perpetual talk about food and drink. Above all avoid speaking of persons, either in the way of praise or blame, or comparison. If you can, win over the conversation of your company to what it should be by your own. But if you should find yourself cut off without escape among strangers and aliens, be silent.
Epictetus, in 'The Golden Sayings of Epictetus'