An expression of exasperation commonly used when one pours sour milk over ones bowl of conflakes in the morning when its bucketing down rain outside and you've got to cycle into work and don't have time to get anything else to eat... and you've been dumped the night before... and you've got a chillblain... and you've lost your place in the book you were reading... and you've got one of those tickly coughs that won't go away.. and you've stepped on an upturned plug in your socks just before.
That stuff you seem to collect deep in your closets or at the bottom level of your garage that you categorize somewhere between crap and treasure. It can often be found as well at the bottom of drawers in old chests and in the corners of attics.
The old guy down the street peruses flea markets on the weekends and brings home a pickup truck filled with diddlepoop.