Someone who suffers from monomania is unhealthily preoccupied with something. If your sister talks about nothing but her collection of vintage lunch boxes, you could call it monomania.
It's one thing to be excited about playing Scrabble or preoccupied with local politics, but when any interest gets out of hand, you can call it monomania. The word monomania, from the Greek mono, "one" and mania2020欧洲杯时间, "madness," was coined by a French psychiatrist in the early 1800s. One of the most famous literary cases of monomania is that of Captain Ahab, obsessed with his pursuit of Moby Dick.