Twihard

Example:He's a complete Seinfeld fanatic who'll watch reruns every day.

Definition:An extreme enthusiast.

Example:She's such a Beyoncé weenie, she always knows every detail of her albums and tours.

Definition:A slang term for a very enthusiastic fan, especially of a pop culture franchise.

Example:My friend is a real Harry Potter buff and can quote the entire film series from memory.

Definition:A person who is very knowledgeable about or skilled in a particular activity or subject.