tilli, I am more than happy to explain how I am disinterested.
Read my lips...."Disinterested" means impartial, not influenced by one's own advantage. (Oxford dictionary). If I did not find the subject interesting, as you suggest, then I would be "Uninterested". Similar words, but very different meanings. Still, plenty of time to study English during your forthcoming retirement. Toodle pip, time for tiffin.