There is a bloke who lives near me that was always the pain in the ass for us roadies in the area. He used to cycle in jeans and a Raleigh top, then eventually progressed to tights. We'd all see him out somewhere on his bike, and we knew he did miles and miles, probably more than we did as he was 'between jobs' for years, and always on the bike.
He'd be cycling along at 12-14 mph, and as you saw him, you'd know that even though you were doing 23-25, he'd latch on as you passed - you couldn't shake him, he would just sit there annoying you - he never spoke, even if you slowed to chat....blooming annoying - still see him these days, 20 years on.
He even chased us in a car with bikes on the roof coming back from racing... total head he ball, but obviously pretty fit, but no idea.