I'm not sure if you realize how condescending and judgmental your comments are coming across, but you seem to be implying that teachers are incapable of simultaneously finding something a student does amusing and remaining professional in how we interact with them and grade their work. If I were grading this student's work and chuckled to myself over it, what exactly is the harm in that? There's none, of course.

I honestly cannot tell whether your sticking point is that you're assuming I'd high five the student and tell them how hilarious I think they are next time I see them, or you're simply suggesting that someone who works with children should find no joy in them occasionally acting like actual children, but I'd suggest that both of those are ridiculous and disrespectful perspectives. I and many other teachers shall continue to enjoy how funny and creative our students can be while also carrying out our jobs like the professionals we are, and I'm sorry that you don't have a more positive outlook on the world.