It's probably semantics, as I was honestly disappointed in the actual student. Actually, I was steamed, especially after being stuck on the phone with his dad for a half hour as he used me as a therapist to explain why his marriage failed and his ex-wife was ruining his son (all laced with a ton of profanity). I probably sugar coated my own feelings to extricate myself from the conversation faster.
Some people object to any kind of personal reaction from you, ie, "I was very disappointed". Maybe in the future you should carefully edit out all personal response and stick to the facts... I think the parents will find that both less personal and more harsh, but they won't be able to say anything against it.
This is the biggest problem with kids these days. Of course dissapointed is an appropriate word. Kids should have to accomplish something before everyone tells them how wonderful they are.