Opening a can of worms usually means "making a bigger problem than the one you were trying to solve", because it is harder to deal with an open can of worms than a closed one. When the can is closed, you at least know roughly how many worms you have and where they can be found. Open the can, and the squiggle all over, and it is nearly impossible to put them back in.
Now..."Piss like a racehorse"...that's one that has always baffled the piss out of me. Are racehorses known for producing more urine than, say, a plough horse? Or is this related to the drug testing they make racehorses endure? I thought that was done via saliva, so shouldn't it in that case be "spit like a racehorse"?
Stupid sayings...
