While screaming like a little girl, I've slammed it into park and I'm getting out of the vehicle. Any attack from the back seat is met with elbows. Drawing while reacting isn't likely an option for me, since my IWB is covered by the seat belt. It's not pretty or flattering, but that's likely what would happen.
Once I'm out of the vehicle, I'm reassessing based on what the occupant has or has not done.