To me it was how he was throwing his fits. Since he is being compared to Bane since they both have weird voices and masks. Bane came off as angry to me, ill compare them. Listening to that little toad chew Bane out, like a boss he just puts his hand on the guys shoulder, gets angry at him, and snaps his neck.
Kylo on the other hand, just goes into a tantrum destroying a computer console and a chair when he gets mad. Came off as much more childish and emo, just the way he was handled, rather than making him feel like a boss, like Bane did, even though Bane had his own problems and flaws as a character.
I view anger as something that can be restrained, and unleashed at a certain moment, on another person, and a tantrum is like wah wah things arent going my way so im going to scream and cry and break stuff, which is basically what Kylo did. He only killed one guy... who was 90... on his knees... and defenseless.