v.1. To damage something or someone, as in an accident: I cracked up the car when I hit a tree. We gave him a remote control plane for his birthday, but he cracked it up on his very first flight.
2. To become damaged or wrecked: The plane cracked up when it hit the ground.
3. To praise someone or something highly, especially incorrectly. Often used in the passive: I am simply not the genius I'm cracked up to be. His friend cracked him up to be a great mechanic, but I thought his work was shoddy.
4. To have a mental or physical breakdown: We were afraid that the pilot might crack up under the stress.
5. To laugh very hard: She cracked up when I told her the joke.
6. To cause someone to laugh very hard: The funny movie cracked us up. The comedian cracked up the audience.