Of course much depends on the company you're keeping. In many households, the talk around the family table might sound different than what comes up while sipping a post-dinner brandy with your friends. And how well you know those friends also makes a big difference. A heated political discussion or a bordering-on-TMI sex discussion might feel more comfortable and therefore more apt to happen when you're with old friends and people you know well. Certain friends, too, will have an impact depending on their inclination to stir up controversy or their allegiance to a specific point of view.
Work colleagues is another category that has an influence on dinner topics. How well we know them, how much power they have over us at the office, and the kind of environment we work together in will all influence the tenor of the evening. For some people 'mixed company' (usually meaning children or people of the opposite sex) will also dictate the topics of conversation.
Sometimes it all depends on what we're in the mood for. A lively and controversial discussion can be a lot of fun and leave everyone energized and with food for thought. And at other times, a quiet, more mellow evening is more appropriate.
Is there a topic you deem too impolite to discuss at dinner? Do you ever invite friends over that you know will clash, just for the liveliness of it? Have you ever forbidden a topic at the dinner table or stopped a controversial conversation in mid-point because it was going too far?