Update - here we go - new intro (thanks to Tef for sparking this): Libertarians are always being hit with dumb, unlikely situations like these to argue against the universal validity of property rights. I think Molyneux answers them marvelously here.
The two scenes begin 1. with a guy hanging from a flagpole outside my window. He kicks in my window to escape from his predicament; and 2. I see a guy in the water drowning and I grab your lifesaver.
From the FDR Blog:
...[W]e can see that the man who kicks in my window would be doing so with a reasonable expectation that I would prefer him to do so rather than fall to his death – just as a surgeon who cuts into my throat while I am choking reasonably assumes that I would prefer him to do so rather than allow me to die.
If permission cannot be reasonably gained about the use of property ahead of time, then it can always be sought after the fact. If I grab a lifesaver from your boat in order to throw it to a drowning man, it scarcely seems reasonable for me to imagine that you would prefer that I let the man drown rather than “steal” your property.
...[I]f you would have preferred that I fall to death my rather than kick in your window, then of course I am liable for the property damage that I have incurred. My “guess” as to how you would want your property to be used has turned out to be false, just as if I had taken your car thinking that you wanted me to, when it turns out that you considered my action to be rank theft.
Naturally, for any of this to occur, a man must be hanging from a flagpole, have no other option than kicking in a window, and the man whose window is kicked in must have preferred that the hanging man fall to his death – and the man who has saved his life by kicking in a window must refuse to pay any and all restitution for the window he has broken.
Such a circumstance will never arise in this or any other universe. The endless pursuit of these topics tells us much more about the limitations of ethicists than it does the limitations of ethics.