The so-called “Curse of the Bambino” was a favorite hobbyhorse [ˈhɑbiˌhɔrs] of my Red Sox-loving grandfather until the team finally won the World Series in 2004.

hobbyhorse
noun [ˈhɑbiˌhɔrs]

Hobbyhorse usually refers to a topic that someone dwells on, returning to again and again, especially in conversation.

the meaning of hobbyhorse was extended to “a subject that someone returns to repeatedly, especially in conversation.” This sense is typically encountered in such phrases as “get on one’s hobbyhorse” or “ride one’s hobbyhorse.”

English