Wick's occasional outbursts of anger are such an underrated aspect of his characterization. Beyond just being something refreshingly different from his usual sweet/sad/scared trinity, I think it shows A LOT about the environment he was raised in.
Wick is a patient man, he only actually breaks down into anger when he's already been pushed to his limit with stress. His grandmother refusing his pleas to spare Thjazi and Tyranny continually ignoring him, his first time on death's door, being insulted (and even punched) constantly by his allies, etc. And when he snaps it only directed at the cause of his frustration (Tyranny disobeying him, Thaisha killing one of the luxes in a spur of the moment, Julien punching him). And when he doesn't have someone in particular to snap at, he just simmers in self-resentment.
When he does lose his temper, it reflects on Yanessa in a couple interesting ways. For one, it honestly makes him resemble Yanessa's aggression a lot. It's quick, it's loud, and it's mean.
But moreso it reflects the effect growing up around her anger had on him and his ability to stand up for himself. He may have been his family's favorite child, but his reaction to Yanessa's outburst in episode 3 reads to me as someone who is used to seeing it and being cowed into submission by it, or seeing others be cowed by it.
It explains a lot about Wick, despite sometimes having misplaced confidence, being so hesitant to actually stand up for himself until his stress boils over into rage and he can't stop himself. Then he usually feels the need to apologize immediately afterword. Being in that environment trained him to be obedient and passive, even in the face of anger and insults.
He never learned to stand up for himself normally, so now he just lets his stress build up continuously until it boils over into aggression.
Angry Wick you'll always be famous I love you.
