1.) A can of crap is a bad, troubling situation arising when a decision or action and produces considerable subsequent problems. If you open a can of crap, you do something that will cause a lot of problems and is probably going to cause more trouble.
2.) A can that is full of crap.
Yeah Frank, I was at the meeting when they read the financial statement, and Frank, if they ever find out we capitalized a loss, it's going to open up a can of crap.