He doesn't like postmen because postmen bring bills which Mommy and Daddy have to pay, which means less money for toys and treats. That's a perfectly reasonable assumption. My dogs like the UPS man because he brings packages for Mommy which makes Mommy in a good mood. They like it when Mommy's in a good mood. My postman delivers my mail 1/2 mile away so my dogs don't know about the bills.