The plane I mentioned was an EMB-120, and was not delayed at the gate, and boarding took all of 10 minutes. We did sit on the tarmac for 20 minutes due to noise abatements. Still, if someone had to go so badly that she couldn't wait 20 minutes, she should have gone again at the gate or considered driving to LAX from SNA instead of flying. And why didn't these two pax get up and go while we were waiting on the taxiway rather than leaping up during the takeoff roll?

The captain can be fined $10,000 by the FAA for having pax up and about. It's for their own safety, and on a plane the size of an EMB-120, it could be for the safety of everyone--the sudden shift of weight of several pax moving from the front to the back during takeoff could significantly impact the takeoff.