A burr in (one's) saddle phrase
A person or thing that repeatedly irritates someone or something or causes trouble for them.
I thought John would be helpful when letting him join our team, but he has turned into a burr in our saddle.
Many see this tax as a burr in the citizens' saddle; however, in the view of the government, it is the only way to keep the economy afloat.
The origin of this phrase is not clear.