For me, It is totally okay for farting in class if that fart has no bad smell.
Farting is unavoidable behavior.
You can fart any time that you want but the smell of it must not affect to others.
I see many female friends often fart in class. They will not tell to other friends.
But some of them whispers to me his/her secret.
It is very funny for me.
So if you want to make a fun class, farting to friends is an answer.
Patnarin029 3EN