Reopen old wounds
Definition 1 of 1
Pro Tip 1/3Emotional Impact
The phrase often relates to emotional pain so use it sensitively to avoid upsetting someone. 
I steered the conversation away to not reopen old wounds related to her divorce.
Pro Tip 2/3Metaphorical Usage
Remember, this phrase is usually a metaphor for emotional, not physical, pain. 
Discussing the failed project might reopen old wounds for the team.
Pro Tip 3/3Conversation Caution
Use it when acknowledging that a subject might cause distress by reminding someone of the past. 
Before we delve into this topic any further, I want to be careful not to reopen old wounds.