From WhatPort80

A commonly-used phrase that describes socially inept nerds, fanboys, cosplayers, slashfic authors, libertarians, anarchists, trekkies—in other words, anyone who fears that the light of day will expose them for the freaks they are. Thus, they still dwell in their parents' basement, living off pizza and energy drinks.

Habitats

While most basement-dwellers do indeed live in a basement, this is not always the case. A basement-dweller needs only to live under the care of their parents long after he or she has the faculties necessary to become a contributing member of society. This includes being a twenty year old unemployed college dropout whose mother pays your rent.

Excluded from the title basement-dweller are people who live with their parents for legitimate reasons. Some examples of this include:

• Living at home between semesters of college or during full-time college study.
• Living at home because of financial problems that do not stem from irresponsibility or laziness.
• Living at home to assist in the care of one's own elderly parents. However one must remember there is a difference between "living with mommy", and "living off of mommy."

However, typically we overlook these exclusions and apply the title "basement-dweller" at will.

Typical basement-dwellers are needlessly burdensome on their parents, demanding (like three year olds) that they continue to live out their sheltered life at home. Most of their time is taken up playing online video games, going to nerdish conventions, eating cheese doodles, and playing D&D. In addition, as completists they spend an inordinate amount of time on the Internets, using IRC, LiveJournal, and arguing vehemently over their particular branch of fandom.

Basement-Dwellers & Trolls

No - not trolls like ED and 4Chan, but the mythical creatures from Scandinavia.

Trolls often suffer from greasy skin and warts - caused by an a lack of washing and living off junk food brought down by their moms every 30 minutes, because they are literally unable to move from in front of their computers. They also suffer from poor eyesight and rotten teeth, caused by the endless glare of the internet and grinding their teeth during flame wars.

Their biggest problem is their weight - they are either grossly bloated or hideously skinny. The ones with neckbeards are funnier, particularly when coupled with moobs.

Of course the majority of basement-dwellers are actually trolls, and vice-versa.

Hikikomori

引きこもり. Japanese basement-dweller.

“	Hikikomori live a nocturnal life, in a deep depressive state, far from social responsibilities ( school, work, family) and activities. Even sexuality is often virtually lived and connected to a sexy manga heroine.	„
—Francesco Jodice, describing the subject of his film

Interestingly enough, hikikomori seem to feel that they've got it worse than their western counterparts. A Japanese basement-dweller will often explain that Japanese culture is so simultaneously repressive and demanding that they've never properly adapted to it, causing them to wet themselves if they venture out into the public. Male hikikomori may also explain that they feel they lack social role models because their fathers are entirely submissive. The large percentage of western basement-dwellers who have to import their Pocky likely beg to differ.

Gallery

Alternate basement setup

A Dweller's worst fear: being discovered outside by the pod people!

Congratulations graduate! Now GTFO!