why do men shave and women dont, why are mens bodies covered in thick black horrible hair but womens skin is completely smooth

Why do women have a vagina and men don't?

Because men have only recently gotten into the notion that shaving is necessary for facial hair.

Not all women's skin is smooth. Try hanging around a hippie commune sometime.

as with both men and women, its herditary genetics and hormones....not all men are covered, not all women are smooth....not all men are smooth and not all women are hairy....

Oh you don't want to know how many women shave themselves very regular! Our skin is not hairless, and some women have more body hair then others. Why do you think the ladyshave was invented?
There are even quite some women with facial hair.. so even though you are right and there is a difference, and men have more body hair then women, don't think that a normal female body is completely smooth....

Testosterone!

"Androgenic hair, colloquially body hair, is the terminal hair that develops on the human body during and after puberty. It is differentiated from the head hair and less visible vellus hair. The growth of androgenic hair is related to the level of androgens (male hormones) in the individual. Due to a normally higher level of androgen, men tend to have more androgenic hair than women.

From childhood onward, regardless of gender, vellus hair covers almost the entire area of the human body. Exceptions include the lips, the backs of the ears, the palms of hands, the soles of the feet, certain external genital areas, the navel and scar tissue. The density of hair – the number of hair follicles per area of skin – varies from person to person."

"Hair follicles are to varying degrees sensitive to androgen, primarily testosterone and its derivatives, with different areas on the body having different sensitivity. As androgen levels increase, the rate of hair growth and the weight of the hairs increase. Genetic factors determine both individual levels of androgen and the hair follicle's sensitivity to androgen, as well as other characteristics such as hair colour, type of hair and hair retention.

Rising levels of androgen during puberty cause vellus hair to transform into terminal hair over many areas of the body. The sequence of appearance of terminal hair reflects the level of androgen sensitivity, with pubic hair being the first to appear due to the area's especial sensitivity to androgen. The appearance of pubic hair in both sexes is usually seen as an indication of the start of a person's puberty. There is a sexual differentiation in the amount and distribution of androgenic hair, with men tending to have more terminal hair in more areas. This includes facial hair, chest hair, abdominal hair, leg and arm hair, and foot hair. Women retain more of the less visible vellus hair, although leg, arm, and foot hair can be noticeable on women. It is not unusual for women to have a few terminal hairs around their nipples as well."
Source and further information:
http://en.wikipedia.org/wiki/Androgenic_hair

Who have YOU been hanging around?

You're generalizing way too much here, especially on the point that mens' bodies are covered with thick black hair; if a blonde guy or a red-haired guy has a hairy body, it most likely won't be black.

As numerous people have already answered you, not all women are smooth and not all men are hairy. If in your personal experience)s), that's what you've been exposed to, then you might want to broaden your horizons a little in order to get a more accurate view of life.

men tend to have more hair as a byproduct of testosterone

I'm a woman who shaves her legs and pubic region
where r men covered in thick, black hair? I've never seen that!
and women's skin isn't always completely smooth - mine isn't.