I was at a dinner party a few months ago when the bloke next to me, on hearing I was a novelist started to tell me all about the novel he was writing. I have to admit I glazed over - I like reading novels, not hearing about them - and I particularly lost interest when he told me he'd only written a couple of pages. I hope he proves me wrong for his sake, but I doubt very much if that novel will ever get written.
Writing a novel requires a lot of energy. 100,000 words or so takes a lot of typing even without the concentration on the story telling. Somehow you have to sustain your energy and enthusiasm for at least several months, if not several years. Story telling is in part a desire to communicate. If you’re doing that communication to all and sundry at dinner parties you’re dissipating the energy you need to keep going with your story. Worse, with frequent telling, you may become bored with your own story before you’ve got it written down.
So don’t tell anyone what it’s about. Keep that desire to yourself, communicate with the page, not chance met strangers. I’m frequently being asked about what I’m working on at the moment, and I usually shrug and say, it's a novel. If some one pushes, I say something about it being more of the same stuff. People give up at that point (if they haven't already). It's not being rude, it's about saving your energy and enthusiasm for the important stuff, the words you're writing, and not the words you're saying.