“A Dog’s Breakfast” Means a Complete Mess

In everyday Australian English, a dog’s breakfast usually has nothing to do with food. It means a complete mess: something untidy, confused or badly done. The expression is not uniquely Australian, but it sounds natural here.

If merging two spreadsheets has scrambled the formatting and data, you can say, “I made a dog’s breakfast of it.” The pattern make a dog’s breakfast of something focuses on doing the job badly, while “It’s a dog’s breakfast” describes the messy result. “I did it very messy” is unnatural; the more neutral alternative is “I made a mess of it.”

https://www.macquariedictionary.com.au/whats-for-brekkie-or-is-it-breaky-or-breakie/
https://dictionary.cambridge.org/dictionary/english/dog-s-breakfast