I'll sometimes tail a stranger* but stay back 20 or 30 feet, way too far to actually draft and too far to create any safety concerns. If it turns out to be a stronger rider than me, I get dropped, but I'll sometimes try to pass and then continue pulling ahead. To stay right on someone's wheel without asking is very socially awkward. All you have to do to initiate a paceline is ask, "You want to work together?" but of course you should then expect to take your fair turns pulling. The situation seldom occurs when I'm alone. Usually, it's when I'm already riding with a friend and we encounter another group of two or more.


* Even this is something I'll only do to another dude. If it's a lady riding alone, I never follow her, because this is likely to make her uncomfortable for obvious reasons.