To vex someone is to bother them in a way that both annoys them and leaves them uneasy — not a flash of anger, but a small irritation that sits there and nags. That double feeling is the heart of the word: annoyed and slightly worried at the same time. A rude noise merely annoys you; a problem you cannot solve, or a question you cannot answer, vexes you. The word is old-fashioned and literary now. Native speakers know it perfectly well from books, and it turns up in a few fixed phrases — 'a vexed question' and 'a vexing problem' mean a hard, unsettled matter that people keep arguing about, and 'vexed' can also describe a person: 'she looked rather vexed'. But in everyday speech people say annoyed, bothered, or irritated instead. If you say 'that vexes me' to a friend, you will sound like a character in a nineteenth-century novel — sometimes people do that on purpose, for a light joking effect. There is an older, stronger use meaning to harass or torment someone over and over — 'vexed by illness all his life' — which you still see in serious writing. And in law, to vex someone is to keep dragging them into court to wear them down; that use is alive and technical. Worth knowing: in Caribbean English, and in West African English, vex is fully ordinary, everyday, and often used as a describing word — 'I'm vex with you' means plainly 'I'm angry with you', with no old-fashioned feeling at all.