Idiom: (To be) a geek
Jim: What are you doing this weekend?
Carl: Well, I think I'm going to study and work on my remote control airplane.
Jim: Really? You are such a geek!
Carl: Yeah, I know. Everybody says that.
Sally: Did you know that Peter has a huge collection of Star Wars and Batman toys? The guy is like 40 years old.
Grace: I know. Peter is a real geek! His whole bedroom is filled with Star Wars stuff.
Meaning: "A geek" is used to describe someone whose life interests and hobbies are strangely centered around things like science fiction movies, computer games, math, the sciences, engineering, etc.
This term is derogatory and is used to tease people or to make fun of them.