A statement often preceeded by "This cannot happen!"
Often followed by the swift death of the thing making the statement.

A favorite of various evil villains and megalomaniacs, usually moments before the hero kicks their butt.
Other variations include:
You cannot defeat me!
You wouldn't dare!
I have it all under control!
There's no escape for you now!
Evacuate at the moment of our triumph? You must be joking!