I find it helpful to “train” people who I think might be tempted to disturb me during a race. Not only do I tell them that I’m planning on watching the Blob Grand Prix at Something, but I tell them why I need other people not to do certain things during the broadcast (it’s amazing how many people accept “my internet friends depend on me being able to discuss this” as complete justification). That way, they understand enough not to disturb me unless absolutely essential (or they have something intelligent and race-related to add) and to expect a certain amount of… …odd… …behaviour. Occasionally I’m lucky enough to convert someone to motor racing, and then there’s the bonus of having someone to discuss it with afterwards!
Of course, for this technique to work, one must be prepared to learn about other people’s hobbies, at least enough that you don’t commit an equivalent faux pas around them. And to generally treat friends and family reasonably well, so that they’re happy to oblige.