INTPs do not care very much about the trappings of outward existence. Largely unconscious of their physical appearance, they may dress oddly/shabbily, neglect personal hygiene, and generally be blissfully ignorant of social norms. Einstein's hair, for example, is a classic case of INTP hygiene. Many male INTPs will simply let their hair go and put it into a ponytail, producing the sterotypical computer guru. There may also a distinctive smell that the INTP does not realize they exude.
Paul James (see his excellent article) has noted accurately that INTPs will pick one favorite style of clothing and wear it for every occasion (2000). For example, Robert Hanssen, an INTP double agent, wore nothing but black suits. He even dissected cadavers in them. More than one INTP has been described by their biographers as a "cartoon caricature" because of their peculiar attire and appearance. As Einstein put it, "Once you can accept the universe as matter expanding into nothing that is something, wearing stripes with plaid comes easy."