"Hot-headed" is an English idiom used to describe someone who is quick to lose his or her temper in any situation. The implication of this idiom is that the person described in this manner is quick to get angry without calmly thinking about the consequences of that anger. As a result, the actions of "hot-headed" people like this when they are in their angered state often get them in trouble. Anger is often associated with heat in many idioms, which is the reason this phrase is used in this manner.
An idiom can be a short phrase or even just a single word that is distinguished by an accepted meaning that is somewhat different than the literal definition of the word or words in question. Popular usage dictates what an idiom means, allowing it to be readily understood by everyone in the culture of its origin. Using these phrases allows a speaker the opportunity to add a little color to a common conversation. One popular idiom used to denote sudden anger is the hyphenated word "hot-headed."
If someone is described with this idiom, it indicates that he or she doesn't have control over their anger. When something displeases a person like this, they tend to act without thinking in response to the circumstances. The idiom also tends to suggest that this is not a temporary state but rather a problem that has bedeviled this person for a long time. As an example, someone might say, "She is so hot-headed that she yells at everyone who tells her something she doesn't want to hear."
Of course, someone who acts in this manner will likely have to answer for the problems caused by their anger. In many cases, such people will fly off the handle at others, even when the people who receive the brunt of their anger might not deserve such behavior. The consequences of such behavior are usually quite significant. For example, consider the sentence, "Someone who is that hot-headed shouldn't be surprised when others don't want to put up with that nonsense."
Many idioms that have to do with anger include some word related to heat, such as someone who "blows off steam" or someone who gets "hot under the collar." In the case of "hot-headed," it can also be used in its noun form. Someone who is a "hot-head" is constantly getting angry at the slightest provocation. Those described with either form generally have serious anger issues.