There is no legal definition in English law as to what constitutes criminal threatening behaviour, so it is up to the courts to decide on a case by case basis. However, if somebody threatens violence against somebody, then this may be a criminal offence. In most countries it is only an offence if it can be proven the person had the intention and equipment to carry out the threat. However if the threat involves the mention of a bomb it is automatically a crime.
Criminal threatening can be the result of verbal threats of violence, physical conduct (such as hand gestures or raised fists), actual physical contact, or even simply the placing of an object or graffiti on the property of another person with the purpose of coercing or terrorizing.
Criminal threatening is also defined by arson, vandalism, the delivery of noxious biological or chemical substances (or any substance that appears to be a toxic substance), or any other crime against the property of another person with the purpose of coercing or terrorizing any person in reckless disregard for causing fear, terror or inconvenience;
"Terrorizing" generally means to cause alarm, fright, or dread in another person or inducing apprehension of violence from a hostile or threatening event, person or object.