get the giggles

informal To be seized by a sudden, prolonged outburst of uncontrollable spasmodic laughter. A: "Mary Sue! What on earth is so funny?" B: "I'm sorry, Ms. Ryan, I just keep getting the giggles! It's because of something Sarah said earlier, hee hee hee!" Stop telling each other such silly things. I don't want one of you to get the giggles in the middle of church! I suddenly got the giggles during our History exam, which was not great timing. I'm lucky I didn't get a demerit!