Being one of the people left behind as California, Las Vegas, Washington, D.C., etc all succumb. The LA footage, particularly, reminded us of 9/11 (collapsing office buildings with people inside.)
LA subway train falling into one of the chasms: imagine being on that train.
Being on the streets of LA while the earthquake is going on. A giant crack appears along the ground and the dirt beneath your feet starts tilting, causing cars to come hurtling towards you at apparently terminal velocity. In the trailers that show that clip, one of the people knocked into the chasm by a falling car SCREAMS.
Basically being anywhere on the Earth at any point in time. If the earthquakes and volcanoes don't get you, you can bet the tsunamis will.
If you're still left alive after the caldera goes off (which will pretty much choke the living shit out of anyone in America, immediately kill any person in the Yellowstone area, and so on), you get front-row seats of a tidal wave going to drown you!
Falling to your death. Too many times to count.
In the scene where the plane in Las Vegas takes off, the guy on the ATC lets out a chilling, painful scream as he is fried alive inside the control tower when the ash cloud hits it.
Imagine making a narrow escape from the disasters that hit your area, arriving at the rendezvous point for your rescue aircraft just in the nick of time with your family, and being flown to the Himalayas.....only to make the horrifying discovery that your assigned Ark was one of the ones that was damaged. I mean, yeah they eventually did manage to squeeze everyone onto the remaining Arks, but still can you imagine the absolute terror of being in that situation?