If someone is homicidal, they are likely to kill a person, or they are in a state of mind where killing a person is in view. Doctors, police, and courts use it in a serious, almost clinical way: a homicidal threat, homicidal rage, a homicidal patient. The word always points at the killing of a human being, not an animal. In ordinary talk people stretch it as dark humour — “this traffic is making me homicidal” — and they do not mean they will murder anyone; they mean they are extremely angry. That joke use is common, but it is not kind in a real, frightening situation, and it is too heavy for careful writing if all you mean is “very cross.”