A person obsessed with water may be referred to as a "hydrophile" or "hydrophilic."
A person who is obsessed with dates is called a "chronophile."
Grammar Nazi
"Otaku", "Weeb", or "Weeaboo".
Well it depends. If you're a man and you're obsessed with another man well it's called being gay. And if you're a girl and you're obsessed with men it's called love!
A person that loves all things French might be called a Francophile.
A person who is obsessed with book is a bibliophile.
It is called pyromania. The person is a pyromaniac, or firebug.
a foot fetish (podophilia). A person with podophilia is a podophile (not to be confused with pedophile).
an obsessed person is somebody who only thinks of one thing and does it all the time
A person that hunts dinosaur bones is called a paleontologist.
Ecocentrism or environmentalism is the ideology that focuses on the protection and preservation of the Earth's natural environment. Those who are obsessed with ensuring the health and sustainability of the planet are often referred to as environmentalists or ecocentric individuals.