From the steam page:

Live a week in the life of "The Postal Dude"; a hapless everyman just trying to check off some chores. Buying milk, returning an overdue library book, getting Gary Coleman's autograph, what could possibly go wrong?

Blast, chop and pee your way through a freakshow of American caricatures in this darkly humorous first-person adventure. Meet Krotchy: the toy mascot gone bad, visit your Uncle Dave at his besieged religious cult compound and battle sewer-dwelling Taliban when you least expect them! Endure the sphincter-clenching challenge of cannibal rednecks, corrupt cops and berserker elephants. Accompanied by Champ, the Dude's semi-loyal pitbull, battle your way through open environments populated with amazingly unpredictable AI. Utilize an arsenal of weapons ranging from a humble shovel to a uniquely hilarious rocket launcher.
Collect a pack of attack dogs! Use cats as silencers! Piss and pour gasoline on anything and everyone! YOU KNOW YOU WANT TO!