Men don't "have to," but it is weird if he does not because EVERYONE, men & women, have nipples.
No, you must not forget that only Hawaiian men with out penises can have have large breast but no nipples
Shaved obvs, hairy nipples look like spiders like bevans
more blood comes to the surface of your skin to try and keep your body warm and heat up the muscles around it. this rush of blood causes the nipples to become hard on both men and women.
No and there is no relationship between breast and nipple size either
Nipples come in all sizes; men's nipples also can range from very small to very large.
We don't. They get hard when it's cold or some women get hard nipples when they are aroused. Same reasons some men have it actually.
Penis (in men) Clitoris, nipples (in women)
Women use their nipples to breast feed their babies.
Both
Yes. Both women and men have thyroid glands.
It is not just Thai women who have large nipples you generally find all Asian women have rather large nipples.