I think Marco Perella said in one interview that he intentionally tried to make The Weasel "borderline demented".
I remember just one situation where Shepherd can react in two ways to your (lack of) actions. In one mission you get to destroy some mechs and if you miss just one of them, you'll see a cutscene with Shepherd chewing you out for being incompetent.
BTW, I downloaded and watched the flics outside the game and I found several videos with Weasel that I never saw in the game. Also, there's a flic with Yo-Yo sleeping.