Google has opened a dedicated thread where you can post examples of poor titles that Google has created in lieu of your HTML title tags. This comes after Google has confirmed the title changes it made to the search results that actually began a week ago Tuesday.
The thread asked you to include the the URL of the page, the title shown, the device type used and any additional feedback, and if possible a screenshot. It does not seem to ask for the query, which I guess is not needed since Google is not using the query anymore for titles.
The complaint thread is located in the Google Webmaster Help forums and you can submit the details there.
John Mueller of Google posted the thread and wrote:
We recently wrote about an update to the algorithms that we use to select titles for search results. The blog posts includes various details on how we generate these titles, why we have such systems, and how HTML from the page itself is taken into account.
We’d love to get your feedback on how this is working for your website, or for a page that you ran across in your day-to-day usage of Google Search. To make it a bit easier, feel free to add your feedback as a reply to this post. Your feedback here helps us to improve our systems, helping to make Google Search easier for everyone, and is always very welcome.
If you’d like to give us examples, please include the URL of the page, the title shown, the device type used (was it on a mobile phone or a laptop?), and any feedback you have…