How honest are you with negative sub notes?

Like obviously I'm not going to write "I hate your class, they're terrible and would not shut up long enough for me to speak even once," but man do I want to.

Given that I'm not going to come back to this class, how honest are you with these? I'll obviously write down the normal things, what work we got through, students that specifically had trouble, etc., but is it too snarky to say something like "your class is one of the most difficult I've had in a long time?"