That one is easy: You won’t shock anyone if you show up at the hospital with dirty underwear. You don’t want a trauma surgeon to say that they have to page the neuro-chir. Get under a doorframe, and put your pants up when your head is safe.
I thought the door frame thing was actually not a good idea? The mantra nowadays is drop, cover and hold on. Which might actually put you in a more precarious situation during said quake.