It means to fuck - but typically in the context where the girl is under the impression that the only reason she's meeting up with the guy is to bang and then dip. It's most often used in frat houses among the boys - especially when they get back from the bars at 4am and couldnt pull anyone from the roster.
I fucking hate spring break at home. All I want is to get a quick neek and send her back home in an uber lux, because I'm a gentleman.
Someone that has a no life and is far too interested in yours. Annoying and a sad case.
Mostly used in a humorous way, not literally.
Sort of an Irish term can be considered slagging.