Rag on
Definition 1 of 1
Pro Tip 1/3Always Negative
The phrase is used to express consistent negative comments and is never used in a positive context. 
He can't stop ragging on the new policy.
Pro Tip 2/3Colloquial Slang
It's informal slang. Not suitable for formal writing or professional contexts. 
I wish you wouldn't rag on me in front of our friends.
Pro Tip 3/3Emotional Impact
Using 'rag on' can sound harsh and may hurt someone's feelings. 
It's not fair to keep ragging on her for a past mistake.