Harp on
Definition 1 of 1
Pro Tip 1/3Negative Connotation
Indicates annoyance or irritation of the speaker towards the subject being repeatedly mentioned. 
She harped on the issue even though we had discussed it many times.
Pro Tip 2/3Emotional Intensity
Shows strong emotion or passion about the subject, possibly leading to its excessive mention. 
His speeches always harp on the virtues of hard work and perseverance.
Pro Tip 3/3Informal Usage
More common in casual conversations than formal writing or speech; can seem out of place in formal contexts. 
In the meeting, he ignored protocol and harped on his pet peeves.