We need to be more aware of personality disorders - which are more prevalent than people realise, say experts.
Prof Eddie Kane, of the Institute of Mental Health, said 4% of people have such a condition, with some studies showing rates as high as 13%.
These vary in severity and in personality disorder type.
People with personality disorders are more likely to end up in prison, commit suicide and have mental health problems.
A personality disorder is defined as a pattern of behaviour that deviates markedly from the individual's culture.
Those with personality disorders repeatedly behave in a way that is not acceptable to the community that they live in and cause distress to themselves, or others.
There is a range of different disorders including borderline, anti-social, paranoid and narcissistic.
Doctors say that one of the reasons they are so difficult to treat is that the disorder is ingrained in a person's behaviour - in the same way that we all have ingrained personality traits.
Dr Kingsley Norton, personality disorder lead at West London Mental Health Trust, said: "We all have personalities and it is difficult for us to change the way we behave if it goes against our personality 'type'.
"For example, a belief that people with personality disorders often have is, 'people cannot be trusted - they will always let you down.'
"This is a core belief to that person and will govern the way that they interact with everybody."
That can lead to unco-operative behaviour that is threatening or aggressive - and can get the person with the disorder into trouble.
Most people with personality disorders do not commit offences.
However, for some it significantly contributes to behaviour that gets them involved in the criminal justice system.
About two-thirds of prisoners meet the criteria for at least one type of personality disorder and they have a higher risk of drug abuse.
Leading experts say the disorders are under recognised - even though the numbers of people suffering from personality disorders is much higher than those with more well known problems, such as schizophrenia.
Prof Kane, director of the Personality Disorder Institute at the Institute of Mental Health, University of Nottingham, said: "Although 4% is the generally accepted figures for prevalence some international studies have shown prevalence as high as 13%.
"But because personality disorder is not a disease it does not attract the sympathy that conditions such as schizophrenia does."
Experts are now trying to train those who are most likely to come into contact with a personality disorder how to recognise the condition to make the situation easier to manage.
This is crucial because the way in which staff interact with someone who has a personality disorder can affect the patient's condition.
Dr Norton said: "If the relationship with a patient is not right, it will affect the condition adversely but relationships can also be a cure. It is therefore very important that staff are trained properly."
Prof Kane has developed a training programme for staff that are most likely to come into contact with those who have personality disorders.
It uses video reconstructions to show the types of situations where staff may encounter someone with a personality disorder and what they can do to keep the situation in control.
So far, the programme has been rolled out to a variety of staff including prison officers, police officers, GP receptionists and nurses.
About 5,000 people will have been trained by 2012. In the future professionals working in education and with younger people are likely to get training.
Prof Kane said it could stop difficult situations escalating: "This training helps people to understand personality disorders.
"It is delivered by a trainer and a person with a personality disorder. Feedback from those with personality disorders has shown that it makes a big difference to their experiences in those situations."