A can of worms
Definition 1 of 1
Pro Tip 1/3Figurative Meaning
The phrase is used to describe a complex problem, not an actual container of worms. 
I didn't mean to open a can of worms with that question.
Pro Tip 2/3Negative Connotation
It typically implies the emergence of many unforeseen problems. 
Discussing politics at dinner often opens a can of worms.
Pro Tip 3/3Use with Caution
Be mindful when using it, as it can imply reluctance to face the issues. 
He avoided the topic so as not to open a can of worms.