In the West of Scotland, the term 'buckled', sometimes referred to as 'backlt' is used to express the action of knees buckling due to laughing to an excessive extent. It is rare that someone will actually 'buckle', yet it is still commonly used.
Judith: OMG, MY CAT JUST DIED. *creys*
Samuel Kensington of Herp Derp Co.: lawl, buckled @ that bitch. actually laughing so much i'm buckled out my skin and my internal organs.