As cynical as hackers sometimes wax about the amount of idiocy in the world, they tend by reflex to assume that everyone is as rational, `cool', and imaginative as they consider themselves. This bias often contributes to weakness in communication skills. Hackers tend to be especially poor at confrontation and negotiation.
Because of their passionate embrace of (what they consider to be) the Right Thing, hackers can be unfortunately intolerant and bigoted on technical issues, in marked contrast to their general spirit of camaraderie and tolerance of alternative viewpoints otherwise. Old-time ITS partisans look down on the ever-growing hordes of UNIX hackers; UNIX aficionados despise VMS and MS-DOS; and hackers who are used to conventional command-line user interfaces loudly loathe mouse-and-menu based systems such as the Macintosh. Hackers who don't indulge in USENET consider it a huge waste of time and bandwidth; fans of old adventure games such as ADVENT and Zork consider MUDs to be glorified chat systems devoid of atmosphere or interesting puzzles; hackers who are willing to devote endless hours to USENET or MUDs consider IRC to be a *real* waste of time; IRCies think MUDs might be okay if there weren't all those silly puzzles in the way. And, of course, there are the perennial holy wars --- EMACS vs. vi, big-endian vs. little-endian, RISC vs. CISC, etc., etc., etc. As in society at large, the intensity and duration of these debates is usually inversely proportional to the number of objective, factual arguments available to buttress any position.
As a result of all the above traits, many hackers have difficulty maintaining stable relationships. At worst, they can produce the classic computer geek: withdrawn, relationally incompetent, sexually frustrated, and desperately unhappy when not submerged in his or her craft. Fortunately, this extreme is far less common than mainstream folklore paints it --- but almost all hackers will recognize something of themselves in the unflattering paragraphs above.
Hackers are often monumentally disorganized and sloppy about dealing with the physical world. Bills don't get paid on time, clutter piles up to incredible heights in homes and offices, and minor maintenance tasks get deferred indefinitely.
The sort of person who uses phrases like `incompletely socialized' usually thinks hackers are. Hackers regard such people with contempt when they notice them at all.