I was recently asked this question, and while I've had some disagreements with coworkers over minor things, I've never had a major disagreement that was noteworthy, so I (to my inevitable detriment) said: "Nothing really comes to mind at the moment but if something like that were to happen, I'd do X, Y, and Z". Given the reaction from the interviewer I doubt I passed. I still have 2 more interviews with this company.