expression
thorn in one's side; pain in the neck; person standing in one's way
Idiomatic expression referring to someone (often a superior or more capable person) whose presence is a constant source of annoyance or obstruction, like a bump on one's forehead that one cannot ignore. Used in informal contexts.
See also: 目の上のこぶ
彼は私にとって目の上のたんこぶだ。
He is a thorn in my side.
あの先輩は目の上のたんこぶで、何かと口出ししてくる。
That senior colleague is a pain in the neck, always butting in.
Literally 'a bump above the eye'; the image of a bump on one's forehead that is always in sight and irritating is used metaphorically for a person who is a constant annoyance, especially one in a position of authority.