I've never had a rider draft me without asking, but if the situation arose I wouldn't be upset or require them to take a pull, unless they joined a paceline. If I'm out alone, I expect to push wind all day long so it's not a big deal. It's preferable for them to announce their presence and intentions, that way I would start pointing out obstacles, rather than just riding by them. In my weekly club rides, I've played the role of a Domestique by pulling dropped riders back up to the group once the group slowed. I don't mind and most people who would want to draft me are probably relatively skilled at drafting. As I'm not a large guy, I actaully offer very little draft benefit. So I probably wouldn't think too much of them ramming or crossing my rear tire.