General terms:
* Hot-headed: This implies a quick temper and a tendency to react strongly to stimuli.
* High-strung: This describes a horse that is easily excited or agitated.
* Nervy: Similar to high-strung, this describes a horse that is easily spooked or anxious.
* Touchy: This implies a horse that is easily angered or upset.
* Difficult: This is a general term that encompasses a variety of behavioral issues, including bad temper.
More specific terms:
* Biting: This describes a horse that uses its teeth to express aggression.
* Kicking: This describes a horse that uses its hind legs to express aggression.
* Rearing: This describes a horse that stands up on its hind legs, often as a defensive reaction.
* Charging: This describes a horse that runs at someone or something aggressively.
Ultimately, the best term to use depends on the specific behavior of the horse.
It's important to remember that a horse's behavior is often a result of its environment, training, and handling. It's best to consult with a professional trainer or veterinarian if you are concerned about a horse's temperament.