Twice. In first grade, during chorus, my class was singing some song. All I remember is that the song's chorus was "Moo Moo milk the cow". My friend and I made eye contact during this part. It started as a snicker, evolved into a snort, and by the end of the song we were rolling on the ground convulsing with laughter, tears streaming down our faces. The teacher kicked us out of class.

The second time was in 8th grade. During homeroom I picked up a random book from the shelf because it had Jerry Seinfeld on the cover and skimmed through it. I ended reading one bit that caused me to descend into uncrontrollable laughter for a good few minutes. No crying. My shrieking laughter did pique the interest of a friend and I showed him the passage. For the next 2 hours every time we made eye contact we both burst into laughter. Each time it increased in hysteria until we were told to leave the room and cool off. I went to the bathroom to splash water on my face. As I looked up from the sink I saw my friend in bathroom mirror. He stares at me and mouths "cotton ball". We both ended up on the ground crying with laughter.

BTW, the passage in question is:

With any kind of physical test, I don't know what it is, I always seem to get competitive. Remember when you were in school and they'd do those hearing tests? And you'd really be listening hard, you know?

I wanted to do unbelievable on the hearing test. I wanted them to come over to me after and go, "We think you may have something close to super-hearing. What you heard was a cotton ball touching a piece of felt. We're sending the results to Washington, we'd like you to meet the President."