Laugh your head off positive verb phrase
When you laugh your head off, you laugh very loudly and uncontrollably.
His story was very funny, so we laugh our head off.
Do you remember Sam? He was the one who made us laugh our head off last year.
Laugh in an uncontrollable way
A loud chuckle or laugh; to laugh noisily
The verb "laugh" should be conjugated according to its tense
The phrase ‘laughing your head off’ dates back to Jacobite times. It was this week in 1747, the 9th of April to be exact, that Simon Fraser, Lord Lovat was executed on Tower Hill in London by John Thrift. Lovat was Chief of Clan Fraser of Lovat and by all accounts he was not a particularly nice man, with a violent streak and a cunning mind. During the ’45 Uprising he forced his son to fight with the Jacobites while he himself professed his loyalty to King George II claiming his sons actions were against his wishes.
Following the Jacobites defeat at Culloden his deceit was soon found out by the government and he was forced into hiding in the Highlands. He was eventually arrested on an island in Loch Morar and transported to London where after a trial lasting five days (in which evidence was given against him by fellow Jacobite John Murray of Broughton) he was sentenced to beheading on 19th March 1747.
Shortly before the execution, a scaffold for spectators viewing the beheading had collapsed and left 20 dead, much to his amusement. Apparently Lovat was laughing about the spectacle as the executioners axe fell. So ended the life of Simon Fraser and the phrase ‘laughing your head off’ was born.
(Source: cullodenbattlefield.wordpress.com)