I don't think you can type someone based soley on appearance, there are so many other influences(like culture) on someone's outward appearance. Some INTPs(in western culture) might have a nerdy or indie/slacker look to them though.
I am not unaccustomed to wearing what I wore to bed two days in a row. This is usually because I have no reason to clean myself. I do my best to look nice in public, but I'd say they only border on 'nice' clothes, not really fancy. I hate shaving.
I do slouch sometimes, though not always (I usually have good posture while walking/standing). When I sit, I either lean back so much I look totally disinterested (I probably am) or, if I get into a conversation I'm into, I slocuh forward and pull my legs up onto the chair and start sitting indian style.
I try to keep it not-too-short not-too-long and basically all my haircuts are just trims, nothing fancy. I clean it every other day in the shower (heard that's better for it and it saves time), and do not dry it, do not comb it, do not brush it. Sometimes I use my hand to put it in a position I like more.
I try to match colors/styles well so I look presentable, but I also like to be able to get ready fairly quickly. I also like to mix casual and formal, so I own a lot of button up shirts (whenever I wear a sweater I like to but a button up under it), have a few vests that I occasionally wear, and about 75% of my jackets are blazers, and most of those that aren't have lapels. Every so often I like to wear a full on suit, usually I do so some random night when a bunch of my friends and I go out (or when it correlates to a special occasion). Sometimes, however, I will wear the same thing a few days in a row (especially pants, which can go longer), particularly if I haven't seen anyone I know while wearing those clothes (obviously, I'll change if it gets visibly dirty). In warmer seasons, it's almost always a t-shirt with some odd picture or reference or a very dry joke on it and jeans. I rarely wear shorts. I also like belts and have worn the same watch virtually every day for about 5 years..
I generally have one pair of shoes at a time that I'll wear almost every day for about a year (until they are clearly falling apart), and a secondary pair for when the first is too different from the rest of my clothes, and a pair of dress shoes I rarely wear. It has been probably 8-10 years since one of these pairs has had shoelaces.
I have had a beard, earlier this year in fact (March-June). It's rare, though, and that's only the second time I ever tried to grow a beard (the first was over summer of 2006). I generally shave every four days or so, so I often look a bit scruffy.
Shower every other day, generally try and use a facial cleanser every day (some days I miss). Obviously, brush my teeth at least twice daily with rare exception.
And, yes, no matter what we do he does generally manage to look rumpled. He has beautiful curly hair with a mind of its own, which has been slowly going away.
“There are two novels that can change a bookish fourteen-year old’s life: The Lord of the Rings and Atlas Shrugged. One is a childish fantasy that often engenders a lifelong obsession with its unbelievable heroes, leading to an emotionally stunted, socially crippled adulthood, unable to deal with the real world. The other, of course, involves orcs.” ~ John Rogers