things you shouldn't admit to

I was dealing with this deaf guy for an hour and a half today. He had a bunch of brain tumours that had taken away his hearing so while he spoke I had to write all of my replies/comments/questions on paper because he couldn't read lips. At the end of our session I cracked a joke (I had to write it down to convey to to him), and he started explaining himself as if he thought I was serious. So then I wrote "that was a joke", and "sorry" and he was like "i know!" as if I was the dumb one. I got really annoyed, because it was really lame to have to write "that was a joke", and just because he had a bunch of brain tumours my joke still deserved some appreciation god dammit.