If you say that someone is temperamental, you are criticizing them for not being calm or quiet by nature, but having moods that change often and suddenly.
"temperamental indifference to neatness""temperamental peculiarities"
2. subject to sharply varying moods;
"a temperamental opera singer"
3. likely to perform unpredictably;
"erratic winds are the bane of a sailor""a temperamental motor; sometimes it would start and sometimes it wouldn't""that beautiful but temperamental instrument the flute"- Osbert Lancaster