Buttons!
I have, for the longest time, tried to to figure out why buttons are on different sides of a garment. Men, usually have buttons on the right side of the garment while women usually have them on the left side. It is not like women have any more chance to be left handed, or anything, so I oft wondered about this phenomena... (OK. Not really a phenomena, but strangeness )
UNDRESSING! That is the answer! When a man undresses a woman (or vice versa), the buttons are on the side their partner is used to!
What a breakthrough!