I hate this saying, or rather; I would call it a phrase. It’s not even a saying. Its like saying “lunch was good” is a saying. “Have fun in class” will never be a saying because it’s fucking stupid. It will never be allowed to have the moniker of a saying because it needs to be banished.
They say it because they have nothing else to add to the conversation. They could say “cool” and it would have the same impact. It’s kind of like me texting someone and being like “Hey, my dog died” and they could be like “cool”, and it would have the same affect as “have fun in class.” Its stupid and pointless and adds nothing to my day other than you acknowledging that I have to go to class at that specific moment. If I tell you that I have to go to class thus why I am leaving our conversation you could say something constructive like “learn something”, still a waste of air, but at least more constructive. Or, you could say nothing at all. example: “Hey, that sounds good, I have to go to class now, so I will talk to you after”. and then you say “…” Nothing. Nothing at all. That would be an appropriate response to me telling you that I have to go.
Other phrases that are not acceptable when a conversation is ending: “LOL”, “Ok”, “Sounds Good”, “:)”.
Who says it? People who are not in school, or even, not in your class. Not once have I ever said to a fellow classmate after a rousing 50-minute power point enhanced lecture “was that good for you?” never. Because it’s stupid. People who tell me to have fun in class have never taken an 8:00 in the morning survey of the anatomy of the brain by, quite possibly, the driest man alive. I can guarantee it. He told maybe one not-material-based joke the entire semester, and even then it was kind of about it. All I want at 8am is to not have pants on. In no way, is that fun. So you know what, all of you, fuck you.
Maybe because in a 9am class about defining what exactly it means to study English at a university level, I’m not drunk. Nor am I in the process of getting drunk. Maybe I should put some vodka in my $4 vitamin water. Perhaps then, and only then, will the phrase “have fun in class” ring true.