He turns into the Hulk when he becomes enraged - not just being angry, but growing angrier too fast.
He’s learned that he can reduce the chances of this happening by keeping himself in a constantly-pissed-off state. Whatever it takes, mentally, to keep himself pissed off - thinking about the unfairness of his condition, dealing with the relative simpletons (almost everybody) fumbling about, etc - he’s doing it. Constantly. He’s effectively increasing the range of his non-Hulky anger.
So if he gets jabbed with something pointy, sure, he’s angry about it. But since he was already angry about “that bitch, over there, eating crackers like she owns the place”, he’s not so much growing angrier as he is refocusing his existing rage on this new annoyance. And apparently that won’t trigger the Hulk-response.
That’s why he’s always gritting his teeth in an wry smile, or wringing his hands, or being snarky - because he’s pissed the fuck off, and trying not to show it.