The worst scene (IMO)
First of all. I love this movie. I rewatch it regularly and enjoy it each time. Despite all the plot-holes and idiot military, it's still one of my favorites. However, there is one scene in particular that always bugs me (no pun intended).
The scene in which Rico runs off to rescue Carmen. I don't mind that he did a personal rescue mission. What I do mind is that he had a squad made up of entirely green recruits with the exceptions of Ace and Watkins. None of the other roughnecks are shown at the muster and only a small handful included the named characters are onboard the rescue ship in the previous battle. This leads me to conclude that the current unit is almost entirely fresh from boot.
What bugs me about the scene is that Rico not only abandons his unit, but he takes the only two known veterans with him, leaving his troops without any sort of command presence or even chain of command outside maybe a squad leader or two that are just as green as the rest. Basically one of two things could have happened. They continued down the bug hole (the most dangerous part of an engagement) and were summarily wiped out, or they did the reasonable thing and fell back to the surface. If it was the latter, Rico is responsible for the deaths of the entire unit. If the latter, any smart person would immediately report his ass, and even Carl couldn't cover up such a dereliction of duty.
Basically, no matter what, Rico commits a major court martial offense in this scene. In reality, he would have faced a serious trial and would likely be given the maximum penalty for his actions (probably hanged). In the film, Carl should have even been under judgement for promoting a guy with only a few engagements to a commissioned officer without first putting him through OCS, (about the only justification Rico has here as he was never taught how to properly be an officer).