The act of throwing a window out of a window.

Not a useful thing to do by any stretch of the imagination, except if you are a performance artist. If you are a performance artist, then for you, meta-defenestration becomes a powerful tool, symbolizing...
um, symbolizing...
think, c'mon...
well, it should be obvious what it symbolizes.

Woundweavr : You're full of crap. But wonderfully so. ;)

Lets see..... it symbolizes....
Oh yeah....
Leaping out the window represents taking daring chances, being innovative, and thinking originally. Throwing things out the window represents rejection.
Throwing the window out the window is our society's growing rejection of ambitious ideas and innovative thought, causing the thrown window to shatter when it lands.

It has already been established that the act of defenestration or throwing something out the window represents an absolute offhand rejection of that thing.

Meta-defenestration, or throwing the window out the window, therefore, represents offhand rejection of offhand rejection, and, thusly acceptance of all points of view.