The ennui that you experience when you are forced to
listen to a boring conversation can be quite excruciating. But you
must at all costs disguise, or dispense with, the physical
manifestations of boredom - yawning, watering eyes, a fixed and
glazed look, frequent glances at your watch, a tendency to cast
your eyes around the room looking for an escape route.
If you have suffered from boredom yourself, you should be all too aware of the manifestations of boredom in others. Never risk being a bore by following these rules: listen carefully to what people have to say; react to their conversation; ask questions; only hold forth if invited to; keep your obsessions to yourself; never lecture or harangue. Above all, be aware that a proper conversation requires the full participation of at least two people.
Some people have been known to pour wine over themselves in a desperate attempt to escape the panicky claustrophobia that is brought on by the bore at the office party, the wedding or the cocktail party. Others have had recourse to lies about mobile phone messages, prior engagements, stomach upsets and domestic emergencies.
The easiest, politest route is to listen silently - raptly, even - for a few minutes, then say, "How fascinating, but please, don't let me monopolise you," tap the next door person and introduce them before making a swift exit, stage right. At a wedding or cocktail party, it's fine to excuse yourself to get a drink or some food, or claim that the host/hostess needs helping - but this is harder in an office situation or in a pub.
If you are trapped by a bore, and you have lost all hope of escape, embrace the situation and try to out-bore the bore, while indulging in an enjoyable venting of spleen. With not a thought for politeness, wrench the conversational initiative away from him/her and start ranting about a subject close to your own heart. It's cathartic to get stuff off your chest and with any luck you'll scare off the bore who's unused to having the conversational baton stolen.