noun. Describes a male, typically young (15 - 35) who is interested to the point of total preoccupation with a hobby that bears the badge of geekdom. Examples include: Dungeons & Dragons, Star Trek, Lord of the Rings, Fantasy Role Playing Games, Science Fiction, Electronics. (It is important to explain that a mere interest in such things does not qualify a particular male, it is only the extreme preoccupation in such subjects that qualifies one as "girl repellant". Qualifying behavior would include dressing up as one's favorite character, attending conventions, or merely devoting an inordinate amount of time to said subjects.
Outlyer cases may also include an individual who displays a complete lack of athletic ability, but who has voluminous knowledge of sports trivia and statistics (note: there is a high correlation with success in fantasy sports leagues). Other correlations include an intellectually gifted male who is physically incapable of performing any athletic task. May also accompany social awkwardness, such as a bizarre laugh, strange mannerisms, public belching and/or an incredible lack of fashion sense (more so than the acceptable lack of fashion sense that nearly every straight male displays).
Those dorks who live down the hall are girl repellant. They're all dressed up in Chewbacca costumes heading to another convention.