We all know people who are self-centred, navel-gazing and egocentric. We also know by now that ‘narcissism’ is shorthand for the sort of people who take main character energy to the extreme. But given that narcissistic personality disorder is a mental health condition, how do we, as armchair observers of others’ behaviour, get a better handle on who’s showing a pattern of consistent, pathological narcissism and who’s just being a bit of an insecure dick?