My favorite is apps that offer a way to cancel a long-running operation, where clicking "cancel" on the confirm dialog cancels the cancellation.

Sydney Padua's awesome, mostly true, steampunk graphic novel "The Thrilling Adventures of Lovelace and Babbage" jokes about the error messages that might have produced by the difference engine. One example occurs when a character tries to stop a sequence that may or may not destroy a precious manuscript:

Annulation lever activated!

Do you wish to continue?

Engage STOP lever to continue. Engage CONTINUE lever to stop.

Time remaining 5..4..3...