Just look him in the eyes and say "NO, you don't".......then walk away. I had this guy that knew me somehow and everytime I saw him he would have to tell me about his last race, or his new car, or his new lift in his new garage, or....... Anyway, he had caught up to me one day and was telling me about the brand new Camaro he had bought and how he wished he could drive it, but it was bought to be a collectible. He had sealed it in a plastic bag in his garage and he wasn't opening it up until it was an antique. THIS and he was still driving the primered, V6 powered second gen Camaro he had owned since I had known him. I also wondered what he did with the pro-street Camaro he was supposed to be building in that garage, but I didn't think it wise to ask. I simply said "NO you don't......and if you do, quit talking about it and pull it out in the road so I can show you what it WON'T do."
Now, he just nods and says "what's up?" when he sees me. It's rude, but so is holding me up and wasting my time just to tell me a lie.