This is my answer. "Bertie strongly dislikes his Aunt Agatha because she treats him poorly" is the best summary of the central idea in the story.
Explanation:
If something is ironic it's unexpected, often in an amusing way. If you're the world chess champion, it would be pretty ironic if you lost a match to someone who just learned to play yesterday. Ironic is the adjective for the noun irony. In contemporary speech, when we call something ironic, we often mean sarcastic.
