止不住的咯咯笑
an occasion when you can't stop giggling
  I got the giggles in the lecture. 我经常在课堂上咯咯傻笑个不停。 
 I got a fit of the giggles in the middle of the meeting.
 He looked so comical and I'm afraid I got the giggles.
 I couldn't look at Klara - I knew I'd get the giggles.
 I got a terrible case of the giggles while she was making the speech.
 See also: giggle noun (LAUGHTER)