I also have one that happened to me a few years ago. There was this manager I complained to. He appeared so respectful and so receptive while listening to my complaint, that I thought I have finally found a good manager who is actually willing to listen.
So after that, over the next few weeks, I brought many more issues to his attention. I was exhaustive with all the details, never have I been more thorough in my life filing complaints, figuring that he would appreciate having all the details. I was also candid and generous with adding my views and feelings as I believe he would be very interested in knowing a customer's perspective on things. As with my first complaint, he appeared to have cared and listened so attentively.
Then one day I overheard that he called me an A, a B, and then a C behind my back while talking to his employees. I felt so betrayed. But I wasn't going to let him shake my faith in the system, though. I complained to his manager.