From: The Golden Sayings of Epictetus (translated by Hastings Crossley) - from Project Gutenberg.
In company avoid frequent and undue talk about your own actions and dangers. However pleasant it may be to you to enlarge upon the risks you have run, others may not find such pleasure in listening to your adventures. Avoid provoking laughter also: it is a habit from which one easily slides into the ways of the foolish, and apt to diminish the respect which your neighbors feel for you. To border on coarse talk is also dangerous. On such occasions, if a convenient opportunity offer, rebuke the speaker. If not, at least by relapsing into silence, colouring, and looking annoyed, show that you are displeased with the subject.