A dog’s breakfast/dinner
Definition 1 of 1
Pro Tip 1/3British Slang
It's British slang, so be mindful of your audience; it might be misunderstood elsewhere. 
I tried explaining cricket to him, but it turned into a dog's breakfast.
Pro Tip 2/3Negative Connotation
The phrase implies a negative view of the state of things, often with a sense of humor. 
His attempt at baking a cake was a dog's breakfast.
Pro Tip 3/3Visual Imagery
Visualize an actual messy dog's meal; it can help convey the disorder metaphorically. 
Look at this room! It's like a dog's breakfast in here.