thorn in the flesh
A constant or persistent cause of annoyance, frustration, or trouble. My little brother is such a thorn in the flesh—he always wants to do stuff with me, especially when I'm trying to hang out with my friends.
thorn in the flesh/one's side, a
A source of constant irritation. This expression appears in several books of the Bible; in the Book of Judges (2:3) it refers to enemies who “shall be as thorns in your sides,” and in the New Testament Paul refers to his infirmities as “given to me a thorn in the flesh” (2 Corinthians 12:7). The term remains current.