When law lecturer Mark Leiser tweeted negative comments about an airline after a flight delay recently, he might reasonably have expected one of two outcomes: either he'd be ignored or he'd get an apology. What he did not expect was that the staff of the company, British airline easyJet, would take matters into its own hands and not let him on the plane.

As he tells it, Leiser was permitted onto the flight he'd booked only when he cited freedom of speech. Of course, then he wrote--again--about his awful experience. EasyJet might say he compounded his offense; I'd say he gave the company a second chance to redeem itself.

Yay! Another Complaint!

Any time customers complain about your product or service, they're doing you a favor. You might not like it but they're sharing their frontline experience of your company, experience that it's quite likely you can't see and therefore can't improve. This feedback is a gift, if, unlike easyJet, you're smart enough to act on.

I remember writing an irate letter to Continental after a particularly painful experience flying from the U.K. to San Francisco. A senior vice president wrote back to me to thank me--yes, thank me--for my feedback. The airline showered me with airmiles and turned me from a critic into a fan.

EasyJet could have done likewise. Leiser offered the company a perfect opportunity to reinforce their positioning as the airline that does not hate its passengers--unlike rival RyanAir. EasyJet might have transformed Leiser from a discontented customer into an enthusiastic evangelist. Instead, it wasted its opportunity and increased its bad publicity.

So how will you respond the next time a customer turns to Twitter? Stoke the anger--or turn it into love?