From Longman Dictionary of Contemporary Englishfit to burstfit to burstBritish English informalLOT/VERY MUCH if you are laughing, shouting etc fit to burst, you are doing it a lot The girls were laughing fit to burst. → fit
Examples from the Corpus
fit to burst• Sam is happy fit to burst.• The yak meat was tough, but after weeks of barley meal we feasted until fit to burst.• When she turned round, her cheeks were fat as balloons, fit to burst.• He had clearly been sobbing fit to burst, but he was now past that.• With a heart fit to burst through tension, at last, a noise. 