1. a polite euphemism for 'bullshit'
2. a general term used in frustration/anger.
Both definitions derive from the early-to-mid 1990's modern art piece by an Italian "artist" who sold cans of his own excrement for $10,000US a unit as it were.
1. The explanation was "crap-in-a-can"
2. "The boss is going to try to make you work overtime tonight." "Crap-in-a-can, I have a date though."