Many cultures and spiritual beliefs actually consider bird poop to be a sign of good luck and a message from the universe.
Fly into his house. Quantum Leap taught me that in some cultures that's considered very bad luck, and in an existential, "your future is ruined" sense, not just the "oh $#!% there's a bird in the house flapping everywhere and $#!%ing on everything" sense.
The same show also suggested not to do so with a friend because that's supposedly good luck again. I suppose having to clean up double bird splatter counts for good karma or something.