Ok, what to do in a situation like follows.
You introduce an innocent topic like "Your favourite food", and the object embarks on "Japanese, in particular, the Nobu restaurant, have you been? it's amazing, the food is great, and, you know, it belongs to De Niro, and there are lots of celebrities there, and I've seen Spice Girls, and it is expensive, they have outlets in Mayfair, and one in Canary Wharf, and all those rich bankers are going..."
Fine, you feel sick within a minute, and you do not want to know anything about this person at all. What to do? Option 1, unproductive, but satisfying, to be an asshole on your own: "That's amazing! How often do you go there?" Option 2, peaceful, but with an unpleasant aftertaste, just smile with random "ah-hum" and run away with the first opportunity.
The problem arises when you are in a quite close non-random company - work colleagues, your club, in-laws convention. How to run away not presenting yourself as a spineless slug, and at the same time stay likable?