Replying to Is laughter involuntary?

so im in french class.
and my teacher hands out pictures of some old french lady.
now my friend awsomo decides to draw a uni-brow and some other shit on it.
at the time i didn't know he did that.
so my other friend looks at it and starts laughing so hard that hes like drooling everywhere and his face is really red.
then from across the room someone says "oh are you thinking about your dad?"
and then me and like a couple other people also start laughing.
then the teacher only sends me and the drooling kid out, and said you can easily control yourself from laughing.
but isnt laughter involuntary?