death by laughter; dying of laughter
Often used hyperbolically to mean laughing extremely hard, not necessarily literal death.
That comedy duo was so funny I thought I'd die laughing.
My friend's story was so hilarious I nearly died laughing.
Compound of 笑い (laughter) and 死に (death). The exact origin is uncertain, but it follows a common pattern of combining a verb stem with 死に to indicate death by that action.