One time in middle school during art class, a classmate told was telling the table (there were 5 of us) the most bizarre story ever and the way he told it was what killed me. I ended up laughing to the point I couldn't breathe right, even the teacher told me to breathe.
Watching Yugioh Abridged. Twice I was laughing so hard I couldn't breathe. First time was when Yugi tagged Atem in to go on a date with Tea leading to a rant that was 95% bleeps and the 2nd time was during the A Very Ishtar Christmas special when random characters would show up to see the newborn baby Jesus.