Vader's angry all the time, don't get me wrong. But even through his anger, his inflection remains calm. The only time he ever resorts to shouting at people is during the beginning of A New Hope.
So hear me out. The Rebels just openly invaded Scarif, destroyed several Imperial starships, stole valuable military intelligence, and handed it off to the Tantive IV. Tantive IV was at the battle. Vader saw with his own two eyes rebel troops running into the Tantive with the plans in their hands, giving it off to them before they flee the battle. No ambiguity at all, Vader saw everything himself.
This was ten minutes ago.
And now the captain of the ship, the very rebel ship Vader just watched break off from a military vessel attacking his fleet, this guy has the audacity to try weasel his way out of it, to Darth Vader, saying it's a councilor ship, on a diplomatic mission to a planet on the other side of the fucking galaxy from where they are now, with no ties to the rebellion whatsoever.
This is the single stupidest asshole Vader ever had to deal with, and he feels like his intelligence has just been personally insulted.