I can see how interchangeably ‘uninterested’ and ‘disinterested’ are used, but the words are very different.
If you are not interested in (or are bored by) something, you’re uninterested. If you do not have a personal stake in something (or are neutral or impartial), you’re disinterested.
John was yawning because he was uninterested in the lecture.
Never think your ex-wife will be disinterested in what you do. 🙂