Have you ever laughed during any serious situation?

I did once in 7th grade when our English teacher was scolding us as we weren't interested in our studies. But while she was scolding I literally laughed but she thought my friend sitting next to me laughed so she scolded him and slapped him too but then he said he didn't do it and I did it. Then she slapped me too and said it is so disrespectful to laugh when a teacher is scolding.