Yes some girls do,and some don't. it really depends on the person.
yes
It's your bu with hairs on it
most boys do it because they want to be cool in some sort of sense they think that......... well no one knows boys not even boys.
Anus Hairs and Butt Cheek Cells.
Why would you need to do that?
Yes
you have a nice butt and they like it.
It is the pattern on the butt of grubs from which hairs grow. Grubs usually become beetles and the different types of beetles can be identified by the rastral pattern of butt hairs on the grub. Here are some good images: http://www.idlab.ento.vt.edu/IDLab/ornimages/rastralpatterns/rastral_pattern.htm
Yes
Maby not a 6 pack but probably some mussel
None.(I hope you do not have any!) 1 jerry zhao