Friendship among women
A woman does not come home one night. The next day she tells her husband that she slept over at a friend's house. The man calls his wife's 10 best friends. None of them know a thing about it.
Friendship among men
A man doesn't come home at night. The next day he tells his wife that he slept over at a friend's house. The woman calls her husband's 10 best friends. Eight of them say he did sleep over and 2 claim he's still there.