When people are narcissistic and have been brought up to think they are wonderful and special, they cannot take any criticism. It makes them angry and resentful. If there is no opportunity or outlet for this, the anger may be turned upon themselves.
More usually, it is mediocre or low exam results, a world's neutral judgement on performance, conflicting with the previous expectation that they will do well, always receive praise that results in a shock to the self-esteem so great that ridding the self that has 'cheated' seems the only answer. It is also an angry response to not receiving what the individual wants.
Every suicide is a tragedy, every one will be followed by an investigation of the reasons. A feeling of worthlessness is common, but in the case of narcissists it may be more the difference between outsiders' ratings of them and their own.