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- a thorn in side
a thorn in side
a thorn in somebody's/something's side
also a thorn in the side of somebody/something someone or something that continually causes problems Most teachers usually have one student in their class who is a thorn in their side. The town finds the casino a thorn in its side, even though it brings huge numbers of tourists to the town. Health inspectors are a thorn in the side of most restaurant owners.