a thorn in somebody’s side | meaning of a thorn in somebody’s side in Longman Dictionary of Contemporary English | LDOCE

From Longman Dictionary of Contemporary Englisha thorn in somebody’s sidea thorn in somebody’s sidePROBLEMsomeone or something that annoys you or causes problems for a long period of time  He’s been a thorn in the side of the party leadership for years. → thornExamples from the Corpusa thorn in somebody’s side• The man has been a thorn in our side since the day he arrived three weeks ago.• Gino was a thorn in their side.