Green’s Dictionary of Slang

1. an intellectual, or one who is considered (negatively) as one.

1967–8		Baker et al. CUSS 161: Neck [...]. [Ibid.] 169: Pencilneck A person who studies a great deal.
1987		C. Hiaasen Double Whammy (1990) 244: Okay, pencil-neck. let’s hear the bad news.
1992		N. Stephenson Snow Crash (1993) 108: Some Yankee pencilneck is looking down his nose at him.
1998		(con. 1986) G. Pelecanos Sweet Forever 66: Tutt entered the locker room shaking his head, wondering when they started letting pencil-necks join this place.
2004		Mad mag. Oct. 53: See our heroine fidget as she cuts loose more and more of the pencil-necks.
2009		(con. 1960s) J. Ellroy Blood’s a Rover 23: More jive on James Earl Ray and Sirhan Sirhan [...] Ray vibed pencilneck. Sirhan vibed towelhead.
2016		T. Robinson Rough Trade [ebook] ‘Listen, pencil-neck [...] get us in there or get her out here’.

2. attrib. use of sense 1.

2001

‘Randy Everhard’ Tattoo of a Naked Lady 61: C’mere, you pencilneck geek!