Why was Dean infected while Sam was safe?

• Dean's a lot scarier than Sam

• Dean seems cockier and more of a bully than Sam

• Sam is immune to all sorts of things -- remember Croatoan?

• Sam's puppy-dog eyes protected him.

• Dean is made of snips and snails and puppy-dog tails (or at least beer and porn and guns), while Sam is made of sunshine and laughter and unicorns.

• I protest! There's no way the ghost should have seen Dean as a dick! Character assassination! IT'S NOT FAIR!