You did not add a country name but since you mention "undergraduate", I guess this is the US - my perspective is French.
I had once this case when teaching (first year of university). I asked once "What is the problem?", and then "Leave the course now" when they were maliciously sniggering again. They tried to explain that I have no right to throw them out, I said "leave now" again and they left.
This did not happen afterward (they were back for the next course).
I think you should take this very seriously. It is a juvenile attempt to see who is stronger, and if you want to have a normal year you should be over the top to show that this cannot happen.
Getting rid of this behaviour is also something you do for other students so that they are not afraid to ask questions.
Disclaimer: this is for France, a country where students come to study and there is no expectation that they are "paying customers". They are students and learn from a teacher, whose role is also to keep the course in one piece.
One note that is probably not relevant: I had a hard time once, as a student, to not burst into laughter when someone asked a question. The question was generic, it is just that we've been teasing each other with other students (yeah, I know) and it was that time when you giggle about anything. I do not believe that this is your case at it seems to be repeated, but a mea culpa just in case.