Focuses on someone's strong and unreasonable attachment or dedication to something. Her grandfather was a train fetishist, investing all his time in model railroads.
Pro Tip 2/3
Not Sexual
Different from the sexual pleasure context; it's about interest or fascination. He's such a grammar fetishist, obsessing over every punctuation mark.
Pro Tip 3/3
Potential Mockery
Sometimes used humorously or sarcastically to poke fun at someone's obsession. My sister, the organization fetishist, labels every single item in her house.