From
gambling, the
bookie's statement that bets taken on an event will no longer be honored. This is usually due to circumstances changing drastically after betting has begun--for example, my old gray
horse can't race, so I'm substituting
Secretariat for her. If I tell the bookies this, they will either cause me
grievous bodily harm, or simply call out that "all
bets are off". Usually prefaced or followed by the statement "You never said anything about X".
Other examples:
If you're
robbing a bank, you should carry a
gun but never use it. Of course, if the
cops show up, all bets are off.
If you're a
cosmic pirate looking to make a little
cash, flying an old man and a farm boy from
Tatooine to
Alderaan is easy money. Of course, if the
Empire is looking for them, all bets are off.