Condescending geek speak for suggesting that your power cord is unplugged. Used to make people with social lives to feel as though they've been bested by a being whose diet consists primarily of Cheetos and Mountain Dew.
User: My computer won't turn on.
IT Guy: Perhaps it's a PEBKAC error, or your AC cable may be experiencing atmospheric impedance.
User: Atmos...? Ooooh! Heh, very clever. I'll have to share that one with my hot girlfriend.
IT Guy: I'm so lonely.