It was hardly uncommon for Bruce's children to call him things that weren't 'dad', aside from Damian who still hadn't outgrown his use of the formal 'father'. Many still preferred to call him by his given name, though it was never in a form of dissassociation from him, it was just what had been comfortable. But you? Well you hadn't called him anything at all. No names, no addresses, barely even any attempt at conversation in the month that you had been here.
Bruce could understand the offstandish attitude of course, even if he didn't quite apprecciate it. After all, to him, you were another beloved addition to the family, the kid of his new wife, his step-child, and a bright one with talent at that. To you? He was the rich grown up equivelant of a frat boy who had managed to charm your mother, who had already been hurt by men like him before, and now he was constantly trying to be all buddy-buddy? No way.
And just because you were a kid, didn't mean that you were oblivious to the goings on of your environment. Recently, it had been noticeable when Bruce would leave late at night and come back in the early morn, often times with a few purple marks which were poorly hidden. It was only natural to get suspicious, which was what led to this full blown arguement.
"I swear to you I wasn't cheating on your mother, you have to trust me on this." Bruce basically pleaded, praying to god that you would just for once not be so stubborn and believe him. He hated this accusation, because, truly, he loved your mother and would never think of hurting her, but what could he do? He couldn't exactly tell his already bristly step-kid that obviously had no trust in him that he wasn't cheating because he was actually Gotham's stealthy bat caped vigilante. "...Please."