If something is obnoxious, it's annoying and unpleasant. Generally, people like to avoid obnoxious folks.
If something is driving you absolutely crazy, it's probably obnoxious. Yelling and stomping your feet is obnoxious. Poking someone repeatedly is obnoxious. Driving like a maniac is obnoxious. If the teacher comes in and finds students jumping up and down and throwing books, she might say, "Stop being so obnoxious!" Any time someone is obnoxious, someone else probably wants them to stop it.