What does "Dog's breakfast" mean?
It means a mess, a botched job, or something thrown together badly. It is about the state of things, not an actual breakfast.
The saying in a sentence
The saying
Dog's breakfast
Example
Work is a dog's breakfast at the moment! We've lost a lot of staff.
When you use it
Use it when a room, a plan, or a piece of work is a shambles.
When you do not
In a formal report, say messy or poorly organised. This one is casual and a bit rude about the result.