If you behave in a melodramatic way, you become more angry, more sad, or more shocked than the situation really calls for. The feeling is big, loud, and a bit like a play. People often use this word to tease or to criticise: they mean “that was a bit much.” It comes from melodrama, old stage plays that mixed music with very strong, simple feelings — heroes, villains, tears. Today it is less about music and more about extra emotion. It can describe a person, a speech, a film scene, or even a sigh. In everyday talk it is common, unlike mellifluous. Though actually, a film scene can be both musical and over-the-top; if you only mean “too much feeling,” this is the word.