“crack somebody up”

[tailin]

When you say”creak him up“，whatdo you mean？

[rewboss]

If something cracks you up, it makes you laugh uncontrollably. Here's a excerpt from a popular British science-fiction TV series:

Doctor: ...I've got to say, I'm such a fan.

Charles Dickens: You're... what?

Doctor: A fan. Your number one fan, that's me.

Charles Dickens: How are you a fan? In what way do you resemble a means of keeping oneself cool?

Doctor: No, no, it means fanatic, devoted. Although, I've got to say, that American bit in Martin Chuzzlewit, what was that all about? Padding or what? I mean, rubbish, that bit.

Charles Dickens: I thought you said you were my... fan.

Doctor: Oh, well, if you can't take criticism... Hey, go on, do the death of Little Nell! Cracks me up every time!

Charles Dickens: [looks horrified]

Doctor: Er, no, forget that...

Dickens is horrified when the Doctor says that the death of Little Nell cracks him up -- makes him laugh -- because it is one of the saddest things Dickens ever wrote.