Had a young fella on a nice looking road bike do that to me once. I was on my old steel road bike that I had fitted with a 2 speed hub on the back (had to - I'm getting old). I had seen him behind for a few miles slowly catching me up. He called "passing" just as we hit a long gradual uphill and I swear he took forever to get by. I looked at him figuring he wanted to chat about my 35 year old bike, but he just stared straight ahead. I gave him the benefit of the doubt by deciding that he must have done a double century before he encountered me. After passing, he slowed, but I didn't have the heart to return the favor. It was just weird.