The flight was from KSAN to KLAX (PEBBLE6-SHIVE1). I briefed this a few times, but each time I tried to start the brief, my captain would stop me and make me change the approach (even though my examiner at the end said I was correct the first time). With the type of aircraft, changing the approach at the last minute and then getting the ATC descent clearance at the same time definitely caused for a loss of situational awareness that I did my best to prevent. During this process, there wasn't much CRM happening, even if I asked questions to my captain.

In hindsight, it was not a helpful tip of the captain to omit the transition on the STAR, but at the time, I deferred to the captain's experience. It didn't sound right doing it, but I didn't trust myself...