laughed my head off.

[keannu]

Is "crack up" similar to "laugh one'e head off"? What other similiar expressions do you have?

3-1p)
W:Shane, did you see Sunday Special on TV last night? I laughed my head off.
M : No, I missed it. I waited all day, but my sister changed the channel.

[Rover_KE]

It cracked me up.

I fell about laughing.

I laughed till I cried.

I nearly died laughing.

[emsr2d2]

"Cracking up" means "to break into laughter and continue that way. "Laughing my head off" suggests raucous, uncontrollable laughter which goes on for an extended period of time.

I laughed my head off.
I nearly died laughing.
My sides almost split.
I laughed my a*s off. (AmE vulgar)
I laughed my t*ts off. (BrE vulgar)
I was crying with laughter.

One of my favourite jokes when I was five:

Q: What goes "Ha ha, bonk"?
Response: I don't know. What goes "Ha ha, bonk"?
A: A man laughing his head off.

Trust me, when I was five, that cracked me up!

[SoothingDave]

Don't forget the internet/text acronym "ROFL" - rolling on the floor laughing.

[Raymott]

"I pissed myself laughing."

[emsr2d2]

The vulgar AmE one also has an internet acronym - LMAO.

You will also hear "I [nearly] wet myself laughing."

[BobK]

...
One of my favourite jokes when I was five:

Q: What goes "Ha ha, bonk"?
Response: I don't know. What goes "Ha ha, bonk"?
A: A man laughing his head off.

Trust me, when I was five, that cracked me up!

Mine was:

Q What goes '99 bonk'?
A A centipede with a wooden leg.

Less to the point than yours!

b