Friendship among women:
A woman doesn't come home one night. The next day she tells her husband she slept over at a friends house. The man calls his wife's 10 best friends. Nine of them know about it.

Friendship among men:
A man doesn't come home one night. The next day he tells his wife he slept over at a friends house. The woman calls her husbands 10 best friends. 8 of them say he did sleep over at their house and 2 claim he's still there.