Kill yourself laughing
Definition 1 of 1
Pro Tip 1/3Colloquial Phrase
Used in casual conversations among friends, not in formal situations. 
At the party, we were killing ourselves laughing at old school stories.
Pro Tip 2/3Figurative Expression
It's an exaggeration; no one is actually harmed or in danger when saying this. 
He told the joke and I was killing myself laughing, though I was fine.
Pro Tip 3/3Emotional Intensity
Indicates a very strong and uncontrollable reaction of amusement. 
Her prank was so good, I killed myself laughing.