How is he being anything but completely reasonable? A bunch of random space marines show up out of nowhere, release a group of prisoners, and all during the middle of a space combat without anyone on board being notified. Then, when the ratling offers up a plan to give them Exactly what they want, one of them starts mouthing off because... what, he isn't the one in charge?

Oh no!!! A space marine isn't going to be the center of attention! However could this possibly be?!

And, yes, he's rude about it. He's a ratling, a guardsmen foot soldier, and a veteran. Anyone who's been around any of the three would know that they aren't 'nice.'

[@Jbcool] If Decius shows up from where the prison scene occurs, he'd be on the lower floor, near Oskar and Vespin's entire squad of ratlings. Everyone else is on a catwalk, a full floor above them, and on the opposite side of the room, save Vespin who is in the middle. Also of note, the room is large, and Vespin has an auto-cannon trained on the other two space marines.