This expression means something that is painful and long-lasting. It comes from the Bible. In II Corinthians 12:7 the Apostle Paul writes: 'To keep me from becoming conceited because of these surpassingly great revelations, there was given me a thorn in my flesh, a messenger of Satan, to torment me.'

Übersetzung:

ein Dorn im Auge sein

Gegenteil(e)

The opposite of "to be a thorn in one's flesh" is "to be the apple of one's eye".

Synonym(e):

You could also say: to be a persistent annoyance.