The bat's name is actually Skip. Skip went out on a bender with his bros, Todd, Rafe and Trevor, and crashed thru Bruce's picture window on the way to the next bar.
"My bad, bro," said Skip. But Bruce didn't speak bat (at the time) and took Skip's crash as a dark omen.
Skip totally should have been arrested and charged with FUI. This would be the first in string of incidents that fed Skip's sense of entitlement.
Now, Skip is President of Bat Country, and most bats hate the shit out of him!
Way to totally screw things up, Bruce Wayne!