Reacting to stress by becoming pale and withdrawn is understandable, but violent or unusual behaviour is nothing more than attention-seeking, teenagers believe.
And while they think it is acceptable to react dramatically to life events, they are less understanding about mental illnesses with physical causes.
Emma Lindley of Manchester University interviewed 18 pupils aged 14-18 about their attitudes to mental illness. She showed them a series of photographs and offered vignettes of information about the people depicted.
A photograph of a teenage girl was accompanied by the information that her name was Sarah and that she had recently begun to have angry outbursts and to cry in the toilets.
The interviewees all showed compassion for Sarah and agreed that there must be a reason for her behaviour, such as domestic violence, divorce or illness in the family.
"The belief that there was a tangible narrative explanation for Sarah's behaviour seemed to make participants feel generally positive and supportive," Ms Lindley said.
"Participants shared the view that Sarah's behaviour was 'normal', in that she was reacting to difficult life events with understandable changes in mood."
Next, interviewees were shown a photograph of teenager Simon. They were told that he regularly joked around and made classmates laugh. But one day he brought three knives into school and started juggling with them, laughing loudly.
Then he sat on the floor, muttering under his breath.
The pupils struggled to show the same compassion for Simon that they had displayed for Sarah. Carrie, an interviewee, said: "The knife thing - it seems like he's yearning to, well, to go a step too far... To be honest, it's verging on crazy."
The pupils believed Simon had chosen to act in this way, possibly out of boredom. They saw his behaviour as an extension of his regular joking - a deliberate attempt at attention seeking.
They concluded that Simon "wants to be noticed, at any cost, to the point of being prepared to sacrifice being normal".
The final photograph showed Jack Nicholson in the film One Flew Over the Cuckoo's Nest. The interviewees were asked to imagine that he lives alone, comes and goes at strange hours, and has been overheard shouting.
Most pupils agreed that this man was potentially dangerous. One pupil, Hardeep, said: "There's a lot of anger in his face." And Aisha said: "That face is well scary... He could just wake up one day and decide to beat someone up."
When asked what kind of threat Nicholson might pose, Hardeep said: "He might kill someone."
The pupils then suggested that he might be schizophrenic, automatically associating schizophrenia with violence.
Ms Lindley concluded that pupils were often prejudiced against stereotypically "mad" behaviour.
Interviewees found it easier to accept mental illness when there was a clear social explanation. By contrast, their attitude to conditions such as schizophrenia - which often have a physical cause - was far more judgmental.
"The idea of a mental illness - say, bipolar disorder - caused by changes in a person's brain chemistry is quite different from the idea of a person's behaviour becoming different in the face of traumatic life events," Ms Lindley said.
"The former is alienating and othering, and the latter humanising and possible to empathise with."
- 'Gateways to mental illness discourse' by Emma Lindley appears in the current issue of the 'International Journal of Mental Health Promotion'.