An unappealing mixture of many things... a hodgepodge... a disorganzined mess... but probably still usable (or consumable in the case of food.) From the idea that a dog will eat anything and feeding it a mixture of whatever is on hand. (Unappealing because only the dog finds its breakfast appealing... if you see or smell the dog food in the morning, as you're feeding the dog, it may well turn your stomach.)
Those contractors didn't do very good work and the made a real dog's breakfast of that job
"dog's breakfast," which has been British slang for "a complete mess" since at least the 1930s. While no one took the time to write down the exact origin of the phrase, the allusion involved seems to be to a failed culinary effort, perhaps a burned or botched omelet, fit only for consumption by the mouth of last resort, Fido. As a vivid figure of speech meaning something so fouled up as to be utterly useless, "dog's breakfast" can cover anything from a play plagued by collapsing scenery to a space mission ruined by a mathematical error. "Dog's dinner," which seems to have appeared around the same time, means exactly the same sort of disaster, but has the advantage of being attractively alliterative. Both phrases are heard occasionally in the U.S., but are more common in the U.K. and Commonwealth countries.
That bedroom looks like a dog's breakfast. Clean it up man!
When you're a in a mad morning rush & dont have time to clean your teeth/deoderise or shower. You only have time for what the dog would do before he went out bum sniffing for the day. A piss & followed by dipping your face in a bowl of water
I woke up at 8.55 & had to go straight to work. I'm proper stinking, cos all i had time for was a Dog's Breakfast