...diss appointments can't be disappointing. There certainly are disappointing diss appointments. Sometimes you discuss points about your diss in a diss point discussion appointment, which, if disappointing, can be a diss point discussion appointment disappointment.

Panel 1:
Parrot and Rasta-Pigeon are talking. Parrot is crying.
RP: Whoa, dude! I’ve never seen you like this. What’s wrong?
P: Prof. Owl said that they wanted to have a talk with me.
Panel 2:
P: ... but when we agreed on a date, they put me into their calendar as “disappointment”.
RP: Oh man, that’s rough. Sorry man.
Panel 3:
Prof. Owl, at their desk
O: Hmmm, shouldn’t Parrot be here by now? I wanted to talk to them about their excellent work and their dissertation. I’m sure I marked “diss appointment” in my calendar.