dad and son argument

[dad arguing to his son about his grades]; (dad); why and how did you get an F- on your report card for each subject?! I am disappointed in you. (son); but i was in the bathroom, dad you gotta belive me; well you weren't in the bathroom for the whole semester, right? Explain to me briefly. well who cares anyway? i get to do whatever i want. (not fake); well then i'm going to get the milk and i'm never ever gonna come back.