Tatsumi wasn't prone to emotional outbursts. A casual observer might even say he wouldn't have recognized emotion if he'd been hit upside the head with a nail bat every time he felt one.
It was why Hisoka didn't mind his company.
It was why he didn't understand his hesitation in talking to Watari about the lab damages; why he didn't understand Watari's reaction to being told his lab funding would be severely restricted; why he couldn't believe when he yelled back, dragging up Watari's past.
Tatsumi wasn't prone to passionate emotional outbursts, but that was what Watari did to him.