Here are the official rules of Shotgun. In case you were wondering.
Though I think there should be an exception that comes into play when someone actually has a shotgun in hand. They should get the seat. This is not included in the rules.
Here is one rule I didn’t know about…
This rule is applied when you have called Shotgun and are waiting for the doors to be unlocked. If you lift the handle while the doors are being unlocked and therefore cause the Shotgun door to remain locked, then you are “voided” for that ride. At this time Shotgun is available for all of the other passengers to call.