Authencity is about being who you are. Brand managers may hate it but if you want to have "a conversation" with your customers, if you want "a relationship" with your customers then best do them the courtesy of treating them like adults.
Ultimately, people like and respect authenticity however horrid you are.
Look at Trump... look at Ryanair, for $!%$'s sake!
For the flipside, see the Andolex post below mangling authenticity and social purpose...
Ditch authenticity as a brand attribute. Don't say you are authentic -- be authentic. "Straight-talking" and "plugged-in" are both better word choices to personify your brand. Attributes should be sufficiently nuanced to drive differentiation through creative expression in a way that will foster a real audience connection.