Most Helpful Guy
By bringing out some callipers and measuring their intracranial cleft distance.
Seriously, it's a gestalt of a million different things, there's little rhyme or reason to it.
At the end of the day, I could suggest a few factors which really chart high: how good your skin is, how cool your hair is, and how neat your clothes are. Also your general demeanour and way of carrying yourself, and what you say or refrain from saying.