how do i tell my partner to stop interrupting or telling one liners when it's not appropriate

today while i'm at the clinic getting assessed for laryngitis the doctor is asking me all sorts of questions and he's either answering them for me, when i want to answer myself or he is trying to be funny when we are trying to communicate. it's like he's stepping on my toes and making the appointment about him, in a weird way. of course i can't tell him when the doctor is there and once we leave the moment has passed. how do i tell him to stop talking before me?