Narcissism och aggression nära hopkopplade
Ett experiment som skulle testa om folk blev mindre aggressiva mot andra om de delade något ( i detta fall födelsedag) visar att narcissister har mycket mer aggressivitet i sig än icke-narcissister.

Läs mer: Cognitive Daily: How to stop arrogant egotists from getting violent
Konrath, S., Bushman, B.J., & Campbell, W.K. (2006). Psychological Science, 17(11), 995-1001.
For participants with low narcissism, there was no difference in aggression, whether their partner had the same or a different birthday (indeed, you can see no bars at all for this group -- it's not an error; the aggression level was zero for both the same birthday and different birthday cases).
Läs mer: Cognitive Daily: How to stop arrogant egotists from getting violent
Konrath, S., Bushman, B.J., & Campbell, W.K. (2006). Psychological Science, 17(11), 995-1001.