be a thorn in your flesh/side

be a thorn in (someone's) side

To be a constant or persistent cause of annoyance, frustration, or trouble. My professor was an environmental activist when he was younger, and, apparently, he was quite a thorn in the oil companies' sides at the time.

See also: side, thorn

be a thorn in your ˈflesh/ˈside

be a person or thing that repeatedly annoys you or stops you doing something: This patient is a real thorn in my side. He’s always complaining of feeling sick and I can never find anything wrong with him.

See also: flesh, side, thorn