As fans, the tip-off than Anakin gets "angry" should be in the first three movies when his hobby is using force choke on high ranking members of the imperial army.
I'd just like to point out that Vader never used his Force choke on any member of the Imperial Army. He seemed generally pleased by the performance of the Army. It was the Navy he hated. And the Imperial officer corps seemed to know this. Other than Ozzel, the wardroom officers of the Executor are seen to cringe and stare at Vader -- even the more junior officers eyeball him behind his back. The Army officers treat him with respect and professionalism; look at how confidently the junior officer briefs Lord Vader on the circumstances of Skywalker's capture in RotJ, the ease with which Veers reports to Vader in ESB. Similarly, the pilot officers in ANH interact with Vader like real professionals. Only the Naval officers act like beaten dogs around Lord Vader.
I'm not sure why Vader had such a distaste for the Naval service. There may have been some residual "brown-shoe" antipathy for the boat-drivers. Or he may have spent the RotS-ANH years primarily among the Army, putting down Jedi cultists and insurgents; or among the starfighter forces, providing precision strikes and close-in protection for Imperial dignitaries -- only dealing with the Navy after he had proved himself worthy of the joint command he seems to exercise. Perhaps Naval officers in the Empire were simply ruder and less competent than their Army counterparts. It certainly seems possible that, in the early Imperial military build-up, one could "purchase" a Naval commission easier than an Army commission -- you just have to bring your own ship!