What a waste ! You lose half the bottle every time !
Not if you do it right...
There is a right way and wrong way.
The right way:
Edited to add that you can do it with a glass as well. I once saw the Belgian version of the Duke of Westminster smash have a dozen crystal glasses trying to do this... *
* When I asked one of the Belgian officers if the cost of the breakages would be added to their mess bill he told me that the private secretary of the chap who broke the glasses would be along to the mess in the morning with a cheque book to pay for the damage.