i've recently switched to a local job in DC and ride metro every day. love it.
when i come across a douchebag/douchebaguette taking up two seats i ask them politely if i could please sit in the other seat. i haven't been turned down (or punched) once. maybe it's just a numbers game and at some point i'll come across some idiot who won't share.
edit: one morning there was a person taking up two seats on a full train and who was/appeared to be fast asleep. i went over and nudged them, hoping to wake them up, and got no reaction. other folks then informed me that they had also tried to wake him up with no success. dunno if the person was truly asleep or just pretending (i.e. ignoring us). either way i didn't care enough to do anything else about it so i stood.
Her punching your head was an appropriate response.
no it was not.