The socks have it
It would be very easy to label a boffin with physical characteristics: Einstein's hair, Patrick Moore's dress sense (not that I'm suggesting Sir PM ever wore a dress), Brains from Thunderbirds glasses. However, that would be shallow.
No. A true boffin would be a person who was wonderfully at home with all sorts of abstract notions. Who has a brain the size of a planet and is able to explain simple facts and phenomena in such complex and technical terms that no-one without and equally sized brain would have a clue what he/she/it was taking about. If they have to lapse into differential equations, tensor algebra or Schwartzian Transforms to "explain" - then so much the better.
A true boffin would also be totally mystified by the inability of us ordinary folk to follow their descriptions and train of thought.
One other thing that a boffin would always do, would be to require strict, technical, definitions and (of course) units of measurement to quantify whatever it is they are referring to - including their own boffinry. I would like to offer the Pyke as a unit of boffinry. 1 Pyke would adequately describe Dr. Magnus, himself. With perhaps a milli-Pyke being the level you attain by wearing mis-matched socks (and 2 mPyke for only wearing one sock). There could, of course, be negative values: attributed to individuals who not only didn't meet the requirements of boffinry, but who actually eschewed them. Being organised, pretty or understandable would count against and that's why there are so few boffins on TV any more.