a burr under someone's saddle
North American informal A persistent source of irritation.Frankly I think the Empress was just being cranky but it irritated me all the same and the incident was still a burr under my saddle today....- I am moved to write you about a book review in your last issue and a closely related subject that has long been a burr under my saddle.
- ‘He has a burr under his saddle,’ I said and the boy turned around, startled.
See parent entry: burr