merchant
n. countable C1 Advanced Oxford US //ˈmɝtʃənt// UK //mˈɜːtʃənt// mer·chant
n. someone who adds a specific word or behavior to everything they do. It is a funny, informal way to describe a person who is obsessed with one thing.
n. a person who habitually engages in or promotes a specific activity or quality. Informal and often used as a suffix-like descriptor to mock someone's repetitive behavior or singular focus.
He is such a gossip merchant.
My brother has become a total gym merchant lately, posting his workout routine every single morning without fail.
In the world of online commentary, he is known as a doom merchant, constantly predicting the collapse of the economy regardless of the actual data.
Usage
Often used in the construction '[Noun] merchant' to create a compound noun describing a person's habit.