geek

A carnival performer specializing in bizarre and unappetizing behavior.

"I once saw a geek bite the head off a live chicken."

A person who is intensely interested in a particular field or hobby and often having limited or nonstandard social skills. Often used with an attributive noun.

"I was a complete computer geek in high school, but I get out a lot more now."

(by extension) An expert in a technical field, particularly one having to do with computers.

"Do you need a hardware geek or a software geek?"

To behave geekishly or in a socially awkward manner, especially when under the influence of drugs or other psycho-active substances, and exhibiting such marked characteristics as hyperactivity, repetitiveness, talkativeness, nervousness, irritability, or paranoia.

"Hey, check out that guy...he's really geeking out pretty bad."