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Phrase(s): *a thorn in someone’s side [and] *a thorn in someone’s flesh
Fig. a constant bother or annoyance to someone. (*Typically: be ~; become ~.) • This problem is a thorn in my side. I wish I had a solution for it. • John was a thorn in my flesh for years before I finally got rid of him.
McGrawhill's American Idioms And Phrasal Verbs