When people would rudely bark at me I like to play dumb.
Me: "I'm sorry, how can I help you?"
Custy: "Paper plates."
Me: "Ok, paper plates. What would you like to know about them?"
Custy: "Where are they?!!" (very flip and rude)
Me: "Oh, okay, see I wasn't sure what you were asking at first... (Drawing it out yet again.) They're in aisle 12, left side, half way down."
Kill them with kindness but don't facilitate their rude behavior. ;)