Our swallows take great delight in aiming their droppings specifically at the washing on the line (especially if it's big white sheets), the car, and yesterday one of the dogs who copped a big splodge. I'm sure they take delight in their accuracy.
They hate the cat and dive bomb her whenever she hangs around outside. In return, she lies on her back pretending to sunbathe, but slyly zaps out a paw if they come too close. It seems like a game for both sides
We have some each year nesting in the hen houses. It seems to be impossible to stop them, but they do seem to be associated with red mite infestations, so we would rather they nested elsewhere (I'm not sure if they bring the mites with them, or simply that when they are there we have a population boost of mites). However, after they have flown all that way from Africa I'm not going to shoo them away

We do knock the nests down after they have gone south for the winter, and use the burner plus diatomaceous earth liberally.
At the beginning of the swallow season we were worried as there were so few birds returning, but now we have a few pairs and lots of young, in spite of the rain