also, slim chance (polite version of the idiom)
- when there is little or no chance of something happening
- used to describe the impossibility of something happening, with a sarcastic undertone
- mostly used as an interjection instead of part of a sentence
- Did you really think that he would show up to work the day after a long weekend? Fat chance!
- "Are you going to buy a new car this year?"
"Fat chance! I can't even afford to fix mine."
- Fat chance of winning the lotto if you don't even buy a ticket.
- "Do you think that we will be allowed to bid on the project?"
"Fat chance! The outcome has already been decided."
- When principal asked to students, "Will it rain today or not"? Tom replied, "Slim chance sir!".
- Doctor told her that being too old there is a slim chance of getting well of her grandfather.
There is a lot of confusion about the origin of the idiom. The meaning is ironic. When the idiom is taken at face value it means that there is a large chance of something happening. Fat means big or large. When it is used in this context, however, it is used sarcastically. This means that the phrase has the opposite meaning to what it seems. It is generally used with a rude tone. When the same message is conveyed in a more polite way we say that there is a "slim chance".