Pigeons only unclean

Birds are the filthy, degenerate hillbilly cousins of dinosaurs that are constantly covered in shit, dirt, blood and disease. Some are less dirty than others, and human garbage introduces new types of filth and disease, but their natural state (like most animals) is disgusting.

IMO, many humans are only marginally cleaner than birds. Some definitely have about pigeon-level self-awareness when it comes to the state of their personal hygiene.