Friendship between women: A woman doesn’t come home one night. The next day she tells her husband that she had slept over at a girlfriend's house.
The husband calls his wife's 10 best friends. None of them know anything about it.

Friendship between men: A man doesn’t come home one night. The next day he tells his wife that he had slept over at a friend’s house. The wife calls her husband's 10 best men friends. Eight of them confirm that he had slept over, and two claim that he was still there.