Sometimes the other characters are what's selling someone's badassitude. Four terrifying martian marines take over the ship... And you still get the impression Holden is more worried FOR them, because he knows what Amos will do to those poor souls if the situation isn't resolved before he gets back.
EDIT: Oh man they're not even marines. It's such a great scene.
Totally love that scene. Both with how little of a shit Bobby gives about the whole thing (and the look on the Martians faces when they realize what she is and could kill them all without breaking her stride), and that everyone is more worried about how Amos will murder them all. They're not even mad about how Alex got roughed up. Nope, it's Amos coming back, seeing the situation and responding by immediately killing everyone.
What's best is they've met Amos, but his demeanor is usually so low key they don't realize he's the one everyone worries about deciding "Well, they've got to die" with the same amount of thought of "Well, got to fix the engines again."