In my latest  BusinessWeek.com column I focus on the need for and power of authenticity in branding. I began the column with the story of Citi, which has been about as inauthentic a brand as there could be over the past couple of years. New CEO Vikram Pandit is claiming to have turned things around, and I hope he has. We’ll see.

Unfortunately, it’s much easier to find examples of brands that are falling down on the authenticity job than those which consistently succeed. That’s why a recent experience I had with Southwest Airlines was so intriguing to me.

A few weeks ago a group of MWC staffers and I were at the Southwest ticket counter checking our bags, and we ran into a particularly nasty agent. She seemed angry at us for simply being there, and scolded us as she rushed us for no apparent reason. There were no long lines, we weren’t late for our flight—we simply offended her by showing up. Or maybe she was just having a bad day.

As we joked about it on the way through security, I noticed how I was interpreting the event differently than I would have if she had worked for, say, American or Delta. In that case it would have been easy to count the bad experience as one more example of how legacy airlines don’t give a rip about their customers. I know I’m overstating it a bit, but  I have come to expect poor treatment from those brands (hey, at least they’re consistent).

In this case, however, I not only gave Southwest a pass, I actually felt sorry for the brand. One of their own was behaving in a way that hurt it, and I didn’t want that to happen. Southwest has been so consistently authentic over the years that the space the brand occupies in my brain simply rejected this one example of rude behavior.

Southwest, like every brand, isn’t perfect. But it is authentic. And that authenticity has built up such equity over time that one bad experience did no damage—in fact, it may have in an odd way enhanced the brand by making me consider why I reacted the way I did. If it happens again soon I may start to reconsider, but for me this experience served as an exception that proved the rule. Kudos to Southwest.