When I first got a cd or a dvd I asked my brother which way up to place it in the slot. He then told me a story about the Irish turf layers whose boss said to them "green side up" and that has now become a standing joke when asking the question "which way up".
An Irish carpenter is nailing up some wooden battens. His mate (also Irish) sees that he is picking up nails from the box but throwing 1/2 of them away.
Hey Paddy' , he says whats wrong with all those nails ?
Paddy replies ' Well Mick, some of them have the point on the wrong end'
Don't be stupid says Mick ' those are the ones for the other side of the wall'