Here is my scenario. I often have to go to my car at night in not so great areas (commuter subway station) where the parking lot lights are always burnt out and sometimes there are people who are obviously not commuters loitering in the parking lot. This, of course, makes me nervous.

I unlock the car door and get in. While I am getting into the seat, I hit the door lock button and shut the door quickly. I then get my keys into the ignition quickly so I am ready to floor it if anyone approaches the car.

The problem is that if I put my keys into the ignition while the door is still open or just after it closes (there seems to be a slight time delay), the door locks unlock themselves. And I think it's all the locks (will double check), not just the driver side even though that is the only one I unlock when I get in. I hate this because anyone can just jump in my car at this point. The manual confirms that the doors can't be locked if the door is open and the key is in the ignition. I guess so that you don't get out of the car, lock it, then find your key still in the ignition. Is there any way to disable this?

 

Take a look at the 'sticky' post 'RX300 FAQ', where Daddy-O has listed the C-BEST settings that control this kind of thing. What you ask does not appear to be there.
Some suggestions:
1. The default setting is '1 press = Drivers door only, 2 press = all doors'.
This is probably the safest combination.
2. Unlock (1 press only) get in, close the door then lock it. THEN put the key in the ignition.
3. Keep your finger on the red panic button when you approach your car.
4. Check underneath the car and the back set when you approach.
5. Find somewhere safer to leave your car - especially after dark in the winter months.

Good luck, and take care out there...